Flintab Ab

Trancom Ab

Krister Karlstrom

Rolf Fabricius-Hansen

Location-representative signals are communicated to vehicles (12, 14, 16) by modifying existing traffic detector stations of the type utilizing an inductive coil (20) embedded in the roadway (22). Circuitry (44-52) is provided for generating a carrier signal modulated in accordance with a modulating signal representative of the location of an associated traffic detector station. A transformer (56) couples the modulated carrier signal into the existing inductive coil such that the coil establishes a magnetic field above the roadway which is modulated by the location representative signals. The vehicles have inductive coils (70) mounted thereon for sensing the modulated magnetic fields, and circuitry (72, 74, 76) for extracting the location-representative signals therefrom. The location-representative signals may then be, e.g., automatically transmitted to a central dispatching station (18).

Vehicle locating system

A communication system is disclosed wherein plural base stations each communicate with plural associated mobile stations in a variable but well disciplined single channel time division multiplexing arrangement. Each base station communicates to and from its associated mobile stations in an associated unitary communication cycle having time segments of variable size but allotted for specific purposes. The mobile stations include clocks which are all periodically synchronized by the base station. The base station transmits cycle timing information at the beginning of each cycle so that the mobiles can determine by referring to their clocks when the various cycle segments begin and end. The number of mobile stations participating in a communication cycle with a given base station can vary as the mobiles move from the service area of one base station to the next. A particular time segment of each cycle is allocated for use by nonparticipating mobiles to transmit requests for participation in the cycles of the associated base station. The mobiles wait a random delay before transmitting their requests in order to reduce the danger of interfering transmissions of two mobiles both requesting participation in the same segment. A central traffic control center mediates the operation of the system, causing the communication cycles of adjacent base stations to occur sequentially rather than concurrently to avoid interference.

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Stockholm, Sweden

Krister Karlstrom