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the main reason that the up-link freq. is higher, is because the freq. and the attenuation have direct relation. The more the freq. the more the attenuation. Because of that we need more powerful devices to send the signal.Because on the earth we are able to equip the facilities easier and there is no weight limitation, we are able to send stronger signal and compensate the attenuation loss.On the other hand, in the down-link, because we have some space and weigh limitations on the satellite we should diminish the attenuation. So, we should reduce the freq. to make a trade-off in that case.
Bear in mind that all these explanations are valid until we are talking about the satcomm. In the mobcomm we should consider all these limitations on the (satellite) mobile phones. Because of that we should choose he lower freq. for the down-link to compensate the attenuation.
Higher frequency means higher energy (E = hf). Thus, the need to reduce energy transmission downlink "in the same band" to reduce the energy required for the purpose of energy saving, because a satellite or a mobile transmission device gets lower energies via batteries or sollar cells unlike trassmission stations where their energy supplies are plentiful.
There is more downlink traffic than uplink traffic.. requests are less intensive than answers.
