Hf Channel Essay

893 WordsNov 9, 20094 Pages
HF Channel Ionsophere is the channel used by the high frequency waves (3-30MHz) for communication. Ionosphere is the highly ionized part of the Earth’s atmosphere which helps in the radio propagation. The structure of ionosphere is highly volatile and depends on a variety of factor like time of day, season, sunspot number, Geomagnetic variations etc. Ionosphere is divided into the following layers D layer It is the innermost layer of the ionosphere between 50-90 km above the surface of the Earth. High rate of recombination renders this layer to be very lightly ionized. It absorbs low frequency rays and thus obstructs communication. E Layer This is the middle layer spreading between 90-140 km in the atmosphere and is highly variable in space and time. It is important for bending most of the signals and reflecting some signals in the lower HF band. It contains larger patches of ionization called sporadic E layer. F Layer F layer is the most important layer for HF communications and with an approximate elevation of 140-400 km. It has the greatest electron density and is the only layer responsible for HF communication at night. F layer is divided into F1 and F2 regions. The lifetime of electrons is greatest in the F2 region. Suitability of HF channel For MIMO For MIMO to result in some kind of gain an important factor is the multipath richness of the channel. This can be deduced from the rank of the channel matrix or the properties of the covariance matrix. If the sub channels are correlated diversity gain reduces. The reduced correlation also means that the independent data streams collapse the rank of the channel matrix to 1 which means that spatial multiplexing is not possible and only beamforming can be used to select the strongest eigenmode of the channel. Ionosphere also offers multiple paths to signals. Such propagation

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