It is necessary to arrange a synchronous satellite every 120 degrees above the equator of the earth, that is, global communication can be realized as long as three synchronous satellites are placed equidistantly on the equator.

Geosynchronous satellites are stationary relative to the ground and located in the equatorial plane and above the equator. On the equator, each satellite signal can cover the range of120, and the central angle corresponding to the equator is 360. Therefore, only three synchronous satellites are needed to be evenly distributed around the world, just covering the whole earth and realizing global communication.