Posts by Justin Bertelsen
Satellite-to-Ground Links (SGL)
A Satellite-to-Ground Link (SGL) describes the communication between a satellite and a ground station. If the ground station is transmitting the signal up to a satellite it is an uplink signal. Similarly, if the satellite is transmitting a signal down to a ground station it is a downlink signal. A basic satellite communication network is…
Read MorePulse Code Modulation (PCM)
Pulse Code Modulation (PCM) is a digital modulation technique used to convert analog information into a binary sequence. Each digit in the binary sequence represents the approximate amplitude of the original signal at that instant. The new digital message signal represents the original signal discretely in both time and amplitude. The basic elements of PCM…
Read MoreGLONASS
Originally designed by the Soviet Union for military communication purposes in the 1970’s, GLONASS is a satellite constellation that has been adapted for commercial uses such as weather broadcasting, navigation, and reconnaissance. GLONASS is often used as an alternative to GPS. The first GLONASS satellite was launched in 1982 and the system was declared fully…
Read MoreField Of View (FOV)
The Field Of View (FOV) is the actual observable area of an optical system like the human eye or a camera. [1] This area is often expressed as the maximum angular size of an optical system as seen from the entrance pupil. Because the entrance pupil is the reference position for the FOV, the defining…
Read MoreConformal VLC Receivers with Photodetector Arrays
At the University of Central Florida (UCF), Pooya Nabavi and Murat Yuksei have designed and prototyped a wide field-of-view (FOV) optical receiver to enable visual light communication (VLC) fro mobile receivers. They used high brightness low power white LED panels and high-efficiency optical transmitters in the VLC system. Time-varying inter-symbol interference (ISI) can be a…
Read MoreInterSymbol Interference
InterSymbol Interference (ISI) is a kind of distortion that occurs when one or more symbols (pulses in digital baseband transmission) interfere with subsequent signals. This can cause noise in the signal which can cause the output to be less than ideal. ISI occurs when there is multipath propagation and/or nonlinear frequency in the channels. These…
Read MoreGEODSS System
The Ground-Based Electro-Optical Deep Space Surveillance (GEODSS) System is a series of space-observing ground stations in the United States and the Indonesian-Pacific. The GEODSS System monitors deep space objects and man-made objects that orbit from 10,000 to 45,000 km above the Earth’s surface. GEODSS was originally established at the White Sands Missile Range in New…
Read MoreFSO Underwater
Free-space optical communications are typically performed in free space, such as air and vacuum, due to the high transmissivity of both mediums in the telecom waveband (1510 to 1600 nm). However, FSO communication can also be performed in non-ideal mediums like water. Categorizing underwater FSO communication as “free-space communication” is possible since no physical link…
Read MorePhased Arrays
Overview A phased array is an array of antennas that can have their beam path steered without physically moving the antennas. This is accomplished by changing the phase angle of the beam using a computerized system. The phase angle can be continuously changed from one angle to the next, enabling the signal to sweep an…
Read MoreModulation Schemes
The following is a list of modulation schemes used in FSO and satcom along with a descriptor of each scheme and examples of practical applications. Analog Modulation Analog modulation deals only with changing the variables of the sinusoidal carrier wave of a sinusoidal signal. It is mainly reserved for teaching purposes, classical applications, and academic…
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