Abstract: An RF receiver comprises a signal processor arranged to perform a method of decoding data contained within a signal that comprises a set of slots, at least one said slot comprising a preamble portion and a payload portion and being transmitted at a predetermined transmission frequency. The signal processor is arranged to perform a first process to derive timing data from the preamble portion and perform a second process to extract information from the payload portion, the second process being triggered from said timing data derived from the first process. The preamble portion comprises at least a first sequence of data and a second sequence of data, and the second sequence is the inverse of the first sequence. In preferred embodiments the first process comprises identifying a transition between said first and second sequences of data and deriving said timing data from the identified transition.

Abstract: The data transmitted from a first station is transmitted at a first data rate. The data transmitted from a second station is transmitted at a second data rate. The second data rate is lower than the first data rate. In view of both the difference in data rates and the synchronization between radio stations, a separate synchronization word is not required to be sent from the second station to the first station on the uplink portion; instead, and because the uplink slots of a given frame are synchronized between transceiving stations, the start of the uplink payload slot can comprise signalling information which simply acts to signify the start of transmission of uplink data from the second station.

Abstract: A method of checking messages from a network of communication sources includes initially testing the signal strength of a plurality of communication sources, storing the identity of the communication sources with the two strongest signals, and alternatively entering a sleep mode and a wake-up mode, the wake-up mode synchronized to the communication source with the strongest signal. The method further includes testing the signal strength of one additional communication source, switching synchronization to the additional communication source if said source presents a signal stronger than the signal of a stored communication source with the strongest signal, and replacing the identity of any stored communication source if an additional communication sources tested in sequence presents a signal stronger than the signal of said stored communication source.

Abstract: An RF receiver comprises a signal processor arranged to perform a method of decoding data contained within a signal that comprises a set of slots, at least one said slot comprising a preamble portion and a payload portion and being transmitted at a predetermined transmission frequency. The signal processor is arranged to perform a first process to derive timing data from the preamble portion and perform a second process to extract information from the payload portion, the second process being triggered from said timing data derived from the first process. The preamble portion comprises at least a first sequence of data and a second sequence of data, and the second sequence is the inverse of the first sequence. In preferred embodiments the first process comprises identifying a transition between said first and second sequences of data and deriving said timing data from the identified transition.

Abstract: A method of checking messages from a network of communication sources includes initially testing the signal strength of a plurality of communication sources, storing the identity of the communication sources with the two strongest signals, and alternatively entering a sleep mode and a wake-up mode, the wake-up mode synchronized to the communication source with the strongest signal. The method further includes testing the signal strength of one additional communication source, switching synchronization to the additional communication source if said source presents a signal stronger than the signal of a stored communication source with the strongest signal, and replacing the identity of any stored communication source if an additional communication sources tested in sequence presents a signal stronger than the signal of said stored communication source.

Abstract: The data transmitted from a first station is transmitted at a first data rate. The data transmitted from a second station is transmitted at a second data rate. The second data rate is lower than the first data rate. In view of both the difference in data rates and the synchronisation between radio stations, a separate synchronisation word is not required to be sent from the second station to the first station on the uplink portion; instead, and because the uplink slots of a given frame are synchronised between transceiving stations, the start of the uplink payload slot can comprise signalling information which simply acts to signify the start of transmission of uplink data from the second station.

Abstract: A vehicle locating unit with improved power management. A receiver receives a signal from a network of communication sources. A signal strength monitoring subsystem determines which of the communication sources are transmitting the strongest signals. A power management subsystem is responsive to the signal strength monitoring subsystem and is configured to alternatively enter sleep and wake-up modes, synchronize the wake-up mode to the communication source transmitting the strongest signal, and test the signal strength of at least one additional communication source according to a predefined sequence.

Abstract: A vehicle locating unit with a receiver for receiving a signal from a network of communication sources, a transponder activated when a communication source sends a message to the receiver, and a power supply regulating circuit for regulating a nominal input voltage and powering the receiver and the transponder. A protection circuit is responsive to an injected input voltage and configured to clamp the injected (high level) input voltage at a predetermined maximum voltage.