Simulation of Real-Time Bit Error Rate in Low Earth Orbit (LEO) Satellites Narrow Band and Wide Band Telemetry Radio Link

While the Low Earth Orbit satellite has been placed on the determined orbit, ground station has required making a contact with satellite to receive information and control its subsystems. The time variant behavior of the satellite –station radio link should be considered in an appropriate model. This issue has been important because of its high impact on choice the type of the modulation, channel access method designing and error control. In this article the probability of error’s range changes would be estimated momentarily. To achieve this purpose, at first instantaneous communication angles have been measured on the satellite theoretically, and based on these communication angles, the momentary gain in transmitter antennas would be determined. Then, the variation of the signalto-noise rate (SNR) have been achieved momentarily and based on it, Bit error rate (BER) changes would be achieved momentarily, during the time which the LEO satellite has been in the direct view of the telemetry receiver antenna. Channels studied in this paper have been wide-band channels which have been used in transferring images and multimedia messages and these channels have been modeled due to the effects of multipath and shadowing conditions

Dual-Band Non-Stationary Channel Modeling for the Air-Ground Channel

Multiple air-to-ground (AG) radio propagation channels are experimentally characterized for two frequency bands, C-band and L-band. These characterizations are aimed to support the specification of the control and non-payload communication (CNPC) links being designed for civil unmanned aircraft systems (UAS). The use of UAS is expected to grow dramatically in the coming decades. In the United States, UAS will be monitored and guided in their operation within the national airspace system (NAS) via the CNPC link. The specifications of the CNPC link are being designed by government, industries, academia and standards bodies such as the Radio Technical Commission for Aeronautics (RTCA). Two bands have been allocated for the CNPC applications: from 5030 to 5091 MHz in C-band and a portion of the aeronautical L-band from 960 to 1215 MHz. The project under which this work was conducted is entitled “Unmanned Aircraft Systems Research: The AG Channel, Robust Waveforms, and Aeronautical Network Simulations”, and this is a sub-project of a NASA project entitled “Unmanned Aircraft Systems Integration in the National Airspace System.” Measurements and modeling for radio propagation channels play an essential role in wireless communication system design and performance evaluation; such models estimate attenuation, delay dispersion, and antenna diversity in wireless channels. The AG channel differs significantly from classic cellular, ground-to-satellite, and other terrestrial wireless channels, particularly in terms of antenna heights and velocity. The previous studies about the AG channels are reviewed and the significant gaps are indicated. NASA Glenn Research Center has conducted an AG channel measurement campaign for multiple ground station local environments, including over sea, over freshwater, desert, suburban, near urban, hilly and mountainous settings. In this campaign, over 316 million power delay profiles (PDPs) or channel impulse responses (CIRs), over 82 flight tracks, have been collected. The measurement equipment was a dual-band single-input multiple-output (SIMO) wideband channel sounding system with bandwidth of 50 MHz in C-band and 5 MHz in L-band. Given the dynamic nature of the AG environments, the channels are statistically non-stationary, meaning that the channel’s statistical parameters change over time/space. We have estimated, via two distinct methods, that the stationarity distance is approximately 15 m—this is the distance over which the channel characteristics can be assumed to be wide sense stationary. The AG channel attenuation is considered as a combination of large scale path loss, small scale fading, and airframe shadowing. The large scale path loss is modeled by both the log-distance model and two-ray models. The theoretical flat earth and curved earth two-ray models are presented, along with their limitations, boundaries and some enhancements. Numerous propagation effects in the AG channels are discussed, and this includes earth spherical divergence, atmospheric refraction, atmospheric gas and hydrometeor attenuations, and ducting. The small scale fading is described by the Ricean distribution, which for unit-energy normalizations are completely characterized by Ricean K-factors; these K-factors are approximately 28.7 dB in C-band and 13.1 dB in L-band. The line-of-sight (LOS) signal can be obstructed by the airplane itself in some specific maneuvers, and this is termed airframe shadowing. For the specific flights and NASA aircraft used in our measurements, the shadowing duration was found to be on average 30 seconds, and the shadowing loss can be as large as 40 dB. The statistics, models and simulation algorithm for the airframe shadowing are provided. The wideband characteristics of the AG channel are quantified using root-mean-square delay spread (RMS-DS), and illustrated by sequences of PDPs. Tapped delay line (TDL) models are also provided. Doppler effects for over water channels are also addressed. Given the sparsity of the diffuse multipath components (MPCs) in the AG channels and generally short lifetime of these MPCs, the CIRs are modeled by the two-ray model plus intermittent 3rd, 4th or 5th “rays.” Models for intermittent ray probability of occurrence, duration, relative power, phase, and excess delay are provided. The channels at C-band and L-band were found to be essentially uncorrelated; this conclusion holds for the specific antenna locations used in our experiments (the aircraft underside), but is not expected to change for arbitrary antenna locations. For the aircraft antenna locations employed, intra-band signals are highly correlated, and this is as expected for channels with a dominant LOS component; analytical correlation computations show interesting two-ray effects that also appear in measurements. Multiple aircraft antennas and carefully selected locations are recommended for mitigating airframe shadowing for the CNPC link. Future work for AG channel modeling includes characterization of L-band delay dispersion and L-band TDL models, estimation of building and/or tree shadowing for small UAS that fly at very low altitudes, evaluation of multiple ground site(s) antenna diversity, and AG channel modeling via geometric techniques, e.g., ray-tracing

Technology requirements for post-1985 communications satellites

The technical and functional requirements for commercial communication satellites are discussed. The need for providing quality service at an acceptable cost is emphasized. Specialized services are postulated in a needs model which forecasts future demands. This needs model is based upon 322 separately identified needs for long distance communication. It is shown that the 1985 demand for satellite communication service for a domestic region such as the United States, and surrounding sea and air lanes, may require on the order of 100,000 MHz of bandwith. This level of demand can be met by means of the presently allocated bandwidths and developing some key technologies. Suggested improvements include: (1) improving antennas so that high speed switching will be possible; (2) development of solid state transponders for 12 GHz and possibly higher frequencies; (3) development of switched or steered beam antennas with 10 db or higher gain for aircraft; and (4) continued development of improved video channel compression techniques and hardware

A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles

In recent years, there has been a dramatic increase in the use of unmanned aerial vehicles (UAVs), particularly for small UAVs, due to their affordable prices, ease of availability, and ease of operability. Existing and future applications of UAVs include remote surveillance and monitoring, relief operations, package delivery, and communication backhaul infrastructure. Additionally, UAVs are envisioned as an important component of 5G wireless technology and beyond. The unique application scenarios for UAVs necessitate accurate air-to-ground (AG) propagation channel models for designing and evaluating UAV communication links for control/non-payload as well as payload data transmissions. These AG propagation models have not been investigated in detail when compared to terrestrial propagation models. In this paper, a comprehensive survey is provided on available AG channel measurement campaigns, large and small scale fading channel models, their limitations, and future research directions for UAV communication scenarios

Ultra-Wideband Phased Arrays for Small Mobile Platforms

This dissertation presents the development of a new class of Ultra-Wideband (UWB) apertures for aerial applications by introducing designs with over 50:1 bandwidth and novel differential feeding approaches. Designs that enable vertical integration for flip-chip millimeter-wave (UWB) transceivers are presented for small aerial platforms. Specifically, a new scalable tightly coupled array is introduced with differential feeding for chip integration. This new class of beam-forming arrays are fabricated and experimentally tested for validation with operation from as low as 130 MHz up to 18 GHz. A major achievement is the study of millimeter wave beamforming designs that operate from 22-80 GHz, fabricated using low-cost printed circuit board (PCB) methods. This low-cost fabrication approach and associated testing of the beamforming arrays are unique and game-changing

Multidisciplinary design and flight testing of a remote gas/particle airborne sensor system

The main objective of this paper is to describe the development of a remote sensing airborne air sampling system for Unmanned Aerial Systems (UAS) and provide the capability for the detection of particle and gas concentrations in real time over remote locations. The design of the air sampling methodology started by defining system architecture, and then by selecting and integrating each subsystem. A multifunctional air sampling instrument, with capability for simultaneous measurement of particle and gas concentrations was modified and integrated with ARCAA’s Flamingo UAS platform and communications protocols. As result of the integration process, a system capable of both real time geo-location monitoring and indexed-link sampling was obtained. Wind tunnel tests were conducted in order to evaluate the performance of the air sampling instrument in controlled nonstationary conditions at the typical operational velocities of the UAS platform. Once the remote fully operative air sampling system was obtained, the problem of mission design was analyzed through the simulation of different scenarios. Furthermore, flight tests of the complete air sampling system were then conducted to check the dynamic characteristics of the UAS with the air sampling system and to prove its capability to perform an air sampling mission following a specific flight path

Experimental L-band SST satellite communications/surveillance terminal study. Volume 5 - Aircraft terminal definition

Aircraft terminal designs for experimental and operational supersonic transport for L band satellite air traffic contro

Technology requirements for communication satellites in the 1980's

The key technology requirements are defined for meeting the forecasted demands for communication satellite services in the 1985 to 1995 time frame. Evaluation is made of needs for services and technical and functional requirements for providing services. The future growth capabilities of the terrestrial telephone network, cable television, and satellite networks are forecasted. The impact of spacecraft technology and booster performance and costs upon communication satellite costs are analyzed. Systems analysis techniques are used to determine functional requirements and the sensitivities of technology improvements for reducing the costs of meeting requirements. Recommended development plans and funding levels are presented, as well as the possible cost saving for communications satellites in the post 1985 era

ATS-6 engineering performance report. Volume 5: Propagation experiments

Propagation experiments at 1550 MHz to 1650 MHz are reviewed, including the Integrated L-Band Experiments system and results, and the Mobile L-Band Terminals for Satellite Communication system. Experiments at 4 GHz to 6 GHz are reported, including the Radio Frequency Interferometer Measurements system and results, and Earth station antenna evaluations. Experiments above 10 GHz are discussed, including Comsat and ATS-6 millimeter wave propagation/experiments, and communication ATS-6 version at 20 and 30 GHz

Compendium of Applications Technology Satellite user experiments

The achievements of the user experiments performed with ATS satellites from 1967 to 1973 are summarized. Included are fixed and mobile point to point communications experiments involving voice, teletype and facsimile transmissions. Particular emphasis is given to the Alaska and Hawaii satellite communications experiments. The use of the ATS satellites for ranging and position fixing of ships and aircraft is also covered. The structure and operating characteristics of the various ATS satellite are briefly described