A satellite providing internet services revolves around Earth in a circular orbit at an altitude of $750km$. A ground station directly below the satellite transmits an electromagnetic signal to it and receives a response signal immediately after the satellite receives the original signal.
Assume that the satellite is directly overhead during the communication, the signal travels at the speed of light, and processing delays and atmospheric effects are negligible.
Calculate the minimum time taken by a signal to travel from the ground station to the satellite and back to the ground station. Compare this with a typical geostationary satellite explaining the justification behind using LEO in place of geostationary satellite taking into account the fact that TVs do operate well without LEOs.
Solution
Since the satellite is directly overhead, the signal travels vertically to the satellite and back to the ground station.
$t_{LEO} = \frac {2\times 750 \times 10^3}{3.0 \times 10^8} = 5.0 ms$
A typical geostationary satellite orbits at an altitude of approximately
$36,000 km$.
The minimum round-trip signal time $t_{GEO} = \frac {2 \times 36,000 \times 10^3}{3.0 \times 10^8} = 240 ms$
The geostationary satellite has an ideal round-trip signal time approximately $48$ times greater than that of the LEO satellite. This illustrates why LEO satellites are advantageous for low-latency internet services.
A geostationary satellite continuously transmits audio and video to many receivers. The television does not need to send a request to the satellite for every frame. A delay of a fraction of a second is generally acceptable, and buffering can smooth out playback. Television broadcasting works well with geostationary satellites because it mainly involves continuous one-way transmission.
Online gaming, video calls, remote control, and many web interactions require frequent exchanges of data. A request travels to a server and a response returns. Longer delays can make conversations less natural, controls less responsive, and applications feel slower. The shorter distance of LEO satellites from Earth reduces signal propagation time, improving responsiveness for two-way communication.