Abstract: A network includes a first transceiving station and a further transceiving station. In one arrangement the data is transmitted from the first transceiving station to the second transceiving station according to a frame structure having a payload portion for payload data and a synchronization portion for synchronization data. The frame structure is selected from candidate frame structures having differing durations of the synchronization portion, according to a data loading factor which depends on the amount of data that is required to be transmitted. The payload capacity may be optimised by reducing the duration of the synchronization portion when a large amount of data is required to be transmitted.

Abstract: In the sending of data in a network from a sending node to a receiving node via a relay node, the receiving node sends a notification arranged to notify both the sending node and receiving node of receipt of data at the receiving node. Notifications acknowledge that the data has been correctly received over each individual stage of transmission, and further acknowledge to the sending node that data has been correctly transmitted over the whole transmission path and received at the receiving node. The burden on the network of sending acknowledgments is reduced while notifications of data transmission over single stages and over the whole transmission path are provided.

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 frequency scanning radar system includes a controller for controlling a frequency generator and a signal processor arranged to determine a Doppler frequency associated with a target. The frequency generator generates three or more sets of signals, each set of signals having a different characteristic frequency and including signals transmitted at a selected rate, and the radar controller selects the rate in substantially direct proportion to the characteristic frequency, whereby to normalize the Doppler frequency determined by the signal processor, such that the normalized Doppler frequency is substantially constant in relation to variation in the carrier frequency. In a frequency modulated radar system, each set of signals includes a sequence of modulation patterns, and the radar controller modifies a given modulation pattern in dependence on the characteristic frequency of the signal being modulated.

Abstract: Electronically steered radar systems such as frequency scanning radars are particularly suitable for detecting and monitoring slow moving, ground-based targets. So-called crawler radar systems are intended for detection of targets that deliberately attempt to avoid detection by keeping low and by moving slowly. Disclosed is a radar system which includes an electronically steered antenna and a receiver arranged to process signals received from a target located at a distance from the radar system so as to identify a Doppler frequency associated with the target. The antenna stares at, rather than glides past, the target surrounding clutter. This means that the spectral spreading of static ground clutter associated with mechanical radar systems can be eliminated, overcoming one of the shortcomings of mechanical radar systems that would otherwise render a crawler radar system unsuitable for Doppler processing.

Abstract: A scanning radar system suitable for detecting and monitoring ground-based targets includes a frequency generator, a frequency scanning antenna, and a receiver arranged to process signals received from a target so as to identify a Doppler frequency associated with the target. The frequency generator generates sets of signals, each set having a different characteristic frequency, and includes a digital synthesiser arranged to modulate a continuous wave signal of a given characteristic frequency by a sequence of modulation patterns to generate one set of signals. The frequency scanning antenna cooperates with the frequency generator to transceive radiation over a region having an angular extent dependent on the generated frequencies.

Abstract: A frequency scanning radar system includes a frequency scanning radar controller for use in controlling a frequency generator, the frequency generator being arranged to generate a plurality of sets of signals, each set of signals having a different carrier frequency and comprising a sequence of modulation patterns, transmitted at a selected rate, wherein the radar controller is arranged to select the rate in dependence on the carrier frequency. The system also includes a signal processor arranged to derive tone data from received signals, wherein the signal processor is arranged to process the received signals at a rate dependent on the rate of transmission of the sequence of modulation patterns. Additionally, the system includes an audio system arranged to output audio data derived from signals received by the frequency scanning radar system by playback of the derived tone data at a constant rate.

Abstract: Embodiments of the invention are concerned with frequency scanning antennas for transceiving radio frequency energy for use in detecting and monitoring ground-based targets. In one arrangement the frequency scanning antenna is embodied as a structure that is capable of steering a radio frequency beam to a plurality of different angles about the antenna structure: the antenna structure comprises at least two array antennas and a controller for controlling input of energy to the two array antennas, and the array antennas are disposed within the antenna structure such that the antenna structure is capable of steering a beam to a first angle using one of said two array antennas and of steering a beam to a second angle, different to said first angle, using the other of said two array antennas.

Abstract: A scanning radar system suitable for detecting and monitoring ground-based targets includes a frequency generator, a frequency scanning antenna, and a receiver arranged to process signals received from a target so as to identify a Doppler frequency associated with the target. The frequency generator generates sets of signals, each set having a different characteristic frequency, and includes a digital synthesiser arranged to modulate a continuous wave signal of a given characteristic frequency by a sequence of modulation patterns to generate one set of signals. The frequency scanning antenna cooperates with the frequency generator to transceive radiation over a region having an angular extent dependent on the generated frequencies.

Abstract: Embodiments of the invention are concerned with a radar system, and relates specifically to scanning radar systems that are suitable for detecting and monitoring ground-based targets.

Abstract: Arrangements according to the invention embody a radio frequency receiver for use in a proximity detecting system, the radio frequency receiver comprising at least one antenna coil operable to receive radio frequency signals; tunable receiver circuitry arranged in operative association with the antenna coil and being arranged to modify the frequency at which radio signals are received by the radio frequency receiver; and a signal processor arranged to amplify and filter signals received by the radio frequency receiver, wherein the radio frequency receiver is operable to receive and process radio signals of frequencies between 100 kHz and 10 MHz. By operating in the low frequency range, multi-path problems associated with high frequency equipment (such as reflections from objects located between the path of the transmitter and receiver) are significantly reduced, whilst distance between transmitter and receiver can be identified extremely accurately.

Abstract: A point to multipoint two-way communications systems in which a base station transmits to a remote station ("outstation") on a frequency derived by the base station from the frequency of a previous transmission received by said base station from said outstation.