The Communications subsystem interfaces with other subsystems in a satellite, mainly electrical to transmit data from satellite to ground station and vice versa. From a physical perspective, it is further divided into:
; * '''On-board or on-satellite Communications subsystem:''' This includes all the devices that are to be placed on the satellite in order to receive signal from ground and also transmit relevant data to the ground. Since the distances of transmission are long (400-36000 km and more), a robust system compromising of antenna and power amplifiers must be present, so that the satellite transmission is properly received on ground and vice-versa.
:* '''Execution point-of-view:''' A satellite must house power amplifiers, transceivers, antennae, memory storage, and if your satellite is not the main payload of the launch vehicle, you have to comply with standard sizes in order to get approval for launch. Also you need to maintain the operating temperature of your electronics in space. A few tasks of communications subsystem:
::# Communications system must match with the required specs of mainly data rate, power transmission and number of signals.
[[File:GMRT2.jpg|thumb|frame|GMRT field. Image reproduced from [https://en.wikipedia.org/wiki/Radio_telescope#/media/File:USA.NM.VeryLargeArray.02.jpg here]]]
[[File:Handheld2.jpg|thumb|frame|Handheld transceivers, which can be used to track the ISS. Image reproduced from [https://commons.wikimedia.org/wiki/File:P25_hand-held_radios.jpg here]]]
; * '''Ground-Station:''' It receives the satellite signal and transmits the control signals to the satellite. On ground, the biggest advantage is liberty and flexibility since there are no rigid size or area constraints. The objective is to reliably receive from and transmit to satellite irrespective of satellite’s current state or weather. The variety in Ground-station setups can be seen from the fact that International Space Station (ISS) reception does not require specialised antennae, whereas deep space missions require GMRT that can go upto the size of football fields. The huge difference in the two above setups is that one receives signals from more than 10000 km away and the other receives them from just 400 km.