The wireless communication is of limited range so that detector means in the base station cause the alarm to be triggered in respect of any particular satellite station when the satellite station becomes located beyond said limited range.
Alarm means (14) are provided in at least the base station, and optionally also in each satellite station.
The data to be transmitted from the satellite station (3) to the central station (1) are superimposed by the present off-load voltage of the satellite station (3) in the form of current pulses.
Central station (1) is connected to a satellite station (3) via a data transmission line (2).
The spoke epoch time comprises one or more dedicated spoke time slots in which only one hub station may transmit to the hub station to the exclusion of all other spoke stations.
A satelite and aground station are in communication with the transmitter and the receiver.
First, when signals transmitted by a first mobile station using a narrowband transmission format are received at a satellite relay station, the received signals are sampled and digitized.