Major elements of Satellite Communications Systems are Satellite, Satellite Launch Vehicle, Satellite Control Centre, Earth Stations, Communication links, User terminals and Network Control Centre. The satellite is composed of three separate units, namely the fuel system, telemetry controls, and the transponder. The transponder includes the receiving antenna to pick-up signals from the ground station, a broad band receiver, an input multiplexer, and a frequency converter which is used to reroute the received signals through a high powered amplifier for downlink.

The primary role of a satellite is to reflect electronic signals. The Power system of the satellite is a combination of solar cells and rechargeable batteries. Most satellites have an on board propulsion system which is used to achieve initial orbit and to make major position changes. Stabilization and attitude control are necessary to ensure that the satellite maintains the proper attitude. Telemetry, Tracking & Command (TT&C) system monitors and controls all other systems on the spacecraft, transmits the status of those systems to the control segment on the ground, and receives and processes instructions from the control segment.

Telemetry components include sensors throughout the satellite to determine the status of various components, the transmitters and antennas to provide the data to the control segment and even the data itself. Satellite Payload is the actual functional block of the satellite, consisting of transponder with microwave receivers, multiplexers, power amplifiers, channel processing and antennas. The ground station transmits terrestrial data in the form of baseband signals which are passed through a baseband processor, an up converter, a high powered amplifier, and through a parabolic dish antenna up to an orbiting satellite. As a receiving station it is converting signals received through the parabolic antenna into a base band signal.

As one transponder provides access to several earth stations/mobile terminals simultaneously, different access methods are followed. ALOHA is the simplest method in sharing a common channel for multiple users but due to collision of transmission from different terminals throughput of pure ALOHA is only about 11%. However, we can achieve 99% throughput using multiple packet transmissions with random delay between packet to packet. An improvement to the original ALOHA protocol is "Slotted ALOHA", which introduced discrete time-slots and increased the maximum throughput up to 37 percent. Time division multiple access(TDMA) is based on the time-division multiplexing(TDM) scheme, which provides different time-slots to different transmitters in a cyclically repetitive frame structure. The advantage in this scheme compared to ALOHA systems is data throughput is 100% and collision free. But the disadvantage is delay of transmission. We cannot send the data real time and have to wait till the allocated time slot comes. Time synchronization is also required among all transmitters to transmit the data in correct time slot. In Frequency division multiplexing(FDMA) channel access scheme, satellite frequency is divided into smaller channels and each user is assigned a specific frequency. Hence, real-time communication is possible. It is simpler to implement compared to TDMA as time synchronization is not required among all transmitters.

The major disadvantage in this scheme is, it occupies larger bandwidth with the increase of number of users. FDMA also supports Demand assignment(DAMA) of channel in addition to pre-assignment(PAMA) for better bandwidth utilization. DAMA protocol enables multiple users to share the limited bandwidth by multiple users by enabling efficient and instantaneous assignment of transponder channels on a first come, first served basis according to data priority. VSAT systems use DAMA for point of sale (POS) transactions, remote location Internet access, mobile maritime communications and military communications.