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Site Diversity
Site diversity is one of six techniques used to improve the reliability of satellite communications by limit atmospheric effects, particularly those caused by rain fade. A diversity scheme is typically required when using frequencies in the Ka, V, or W-band. The downlink transmissions of satellites cover very large areas, that will have different weather. The site diversity technique consists of linking two or more ground stations receiving the same signal: this way, if the signal is heavily attenuated in one area, another ground stations can compensate it. These intense rain areas, for example, supercells, often have a horizontal length of no more than a few kilometers: putting the ground stations at a sufficient distance the possibility of rain fade in the downlink signal will be reduced. The configuration works when the attenuation is not great at the two stations simultaneously. This is usually a valid assumption. Site diversity systems have been known to minimize disruption o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Downlink
In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or shares a physical link with other telecommunications links. A telecommunications link is generally based on one of several types of information transmission paths such as those provided by communication satellites, terrestrial radio communications infrastructure and computer networks to connect two or more points. The term ''link'' is widely used in computer networking to refer to the communications facilities that connect nodes of a network. Sometimes the communications facilities that provide the communication channel that constitutes a link are also included in the definition of ''link''. Types Point-to-point A point-to-point link is a dedicated link that connects exactly two communication facilities (e.g., two nodes of a network, an in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Supercell
A supercell is a thunderstorm characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. Due to this, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms (supercell, squall line, multi-cell, and single-cell), supercells are the overall least common and have the potential to be the most severe. Supercells are often isolated from other thunderstorms, and can dominate the local weather up to away. They tend to last 2–4 hours. Supercells are often put into three classification types: classic (Normal precipitation level), low-precipitation (LP), and high-precipitation (HP). LP supercells are usually found in climates that are more arid, such as the high plains of the United States, and HP supercells are most often found in moist climates. Supercells can occur anywhere in the world under the right pre-existing weather conditions, but they are most common in the Great Plains of the United State ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diversity Scheme
In telecommunications, a diversity scheme refers to a method for improving the reliability of a message signal by using two or more Channel (communications), communication channels with different characteristics. Diversity is mainly used in radio communication and is a common technique for combatting fading and co-channel interference and avoiding error bursts. It is based on the fact that individual channels experience different levels of fading and interference. Multiple versions of the same signal may be transmitted and/or received and combined in the receiver. Alternatively, a redundant forward error correction code may be added and different parts of the message transmitted over different channels. Diversity techniques may exploit the multipath propagation, resulting in a diversity gain, often measured in decibels. Diversity techniques The following classes of diversity schemes can be identified: * Time diversity: Multiple versions of the same signal are transmitted at dif ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diversity Combining
Diversity combining is the technique applied to combine the multiple received signals of a diversity reception device into a single improved signal. Various techniques Various diversity combining techniques can be distinguished: * Equal-gain combining: All the received signals are summed coherently. * Maximal-ratio combining is often used in large phased-array systems: The received signals are weighted with respect to their SNR and then summed. The resulting SNR yields \sum_^SNR_k where SNR_k is SNR of the received signal k. * Switched combining: The receiver switches to another signal when the currently selected signal drops below a predefined threshold. This is also often called "Scanning Combining". * Selection combining: Of the N received signals, the strongest signal is selected. When the N signals are independent and Rayleigh distributed, the expected diversity gain has been shown to be \sum_^\frac, expressed as a power ratio. Therefore, any additional gain diminishes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
