| 摘要 |
<p>A selective call system comprising a system controller (10) connected to a base station transceiver (12) and a plurality of secondary stations (SS1, SS2) equipped with receivers and low powered transmitters capable of sending signals as spread spectrum signals. In order to avoid the near/far problem affecting the reception of signals at the base station transceiver (12) and to avoid applying transmitter output power control on the transmitters of the secondary stations, invitations are issued by the system controller for the secondary stations to respond to, but the power output of the base station transceiver is increased in steps between lower and upper limits so that only those secondary stations receiving the invitation signal are able to respond. In any one set of invitations, a secondary station is only permitted to respond once. Thus the received responses have a strength which lie in a comparable range which avoids the need for power control.</p> |
