Fundamentals

Satellite communication uses an artificial satellite as a repeater or relay that receives an uplink, amplifies, frequency-converts and processes it in a transponder, and retransmits a downlink to one or more earth stations.

Satellite link: earth station A transmits an uplink; the transponder relays a downlink to earth station B.

Term	Meaning
Uplink	Earth station $\to$ satellite
Downlink	Satellite $\to$ earth station
Transponder	Receives, amplifies, converts frequency and retransmits

Typical uses: TV/radio broadcasting; long-distance telephony and data; Internet backbone and rural connectivity; VSAT networks for banks and remote sites; mobile satellite services; and navigation, weather, remote sensing and disaster communication.

Advantage	Reason
Wide coverage	One satellite covers a very large area
Broadcast capability	The same signal reaches many receivers at once
Reaches remote areas	No terrestrial cable infrastructure needed
Rapid deployment	Suited to emergency and temporary networks
Distance-insensitive cost	Cost varies little with distance within coverage

Advantages of satellite communication.

Limitation	Reason
High propagation delay	Long path, especially GEO ($\approx250\,ms$ round trip)
High space-segment cost	Launch and satellite construction are expensive
Large free-space loss	Very long distance $\Rightarrow$ high path loss
Rain attenuation	Serious at Ku/Ka and higher bands
Limited satellite power	Transponder power and bandwidth are finite

Limitations of satellite communication.