| 摘要 |
A system is described for communication by means of signals in form of electromagnetic waves, especially microwaves, within a restricted communication area (3, 7) comprising at least one first unit (4, 6) for emitting a first enquiry signal and receiving a number of reply signals and a number of further units in form of transponders (1, 2, 8) emitting these reply signals when being present in the communication area. The transponders are equipped with modulating means (25, 26) for modulating the arriving enquiry signal with individual reply codes containing information and means for emitting this information as a reply signal. The system is primarily characterized of that each transponder modulating means (26, 72) is adapted to continuously be supplied with its individual reply code from a memory (28) within a first relatively short interval (19) being continuously repeated with relatively long intervals (18), the reply code thus being available to be emitted together with the reply signal in time, completely independent of the enquiry signal. In a preferred embodiment of the system a means is established in the transponder to randomly or pseudorandomly generate said intervals (18). |
