The differentiation of uplink and downlink carrier is important in

In satellite telecommunication, a downlink is the link from a satellite down to one or more ground stations or receivers, and an uplink is the link from a ground station up to a satellite .

Uplink refers to the signal leaving your device and returning to the cell tower , while downlink refers to the signal coming to your device from the cell tower. All cellular devices, including smartphones and tablets, work within 3G, 4G, 5G RF (radio frequencies).31 Mar 2020

It say basically the power at ground stations is more as compared to power available at satellites.So generally frequency for uplink is kept higher than the downlink . There is greater attenuation due to rain when the signal frequency is high.so downlink is also kept at lower frequency.

The uplink frequency is the frequency which is used for transmission of signals from earth station transmitter to the satellite. The downlink frequency is the frequency which is used for transmission of signals from the satellite to the earth station receiver.