Why uplink and downlink frequency are not same in satellite?

Uplink frequency is the frequency at which, the first earth station is communicating with satellite . The satellite transponder converts this signal into another frequency and sends it down to the second earth station. This frequency is called as Downlink frequency.

In case of FDD (Frequency Division Duplex) LTE downlink channel (DL, eNB transmits UEs receive) and uplink channel (UL, UEs transmit eNB receives) are transmitted simultaneously on different frequencies . Also each band is marked by LTE release number where it was defined.

It’s because lower frequencies get reflected by atmospheric bands and cannot penetrate to get through to the satellite . … Therefore, mobile-to-base station (uplink) frequencies are lower than base station-to-mobile(downlink) frequencies.

Mathematically, Frequency = f = c/λ . The frequency is expressed in “per second” or “Hertz”, abbreviated as Hz. In real life networks, the frequency is expressed in Megahertz (MHz) or Gigahertz (GHz).