Abstract

In sending data in a network from a sending node to a receiving node via a relay node, it is convenient to send notifications acknowledging that the data has been correctly received over each individual stage of transmission, and further to send notifications acknowledging to the sending node that data has been correctly transmitted over the whole transmission path and received at the receiving node. However, sending notifications acknowledging such receipt places a burden on the network. The present invention provides a receiving node adapted to send a notification arranged to notify both the sending node and receiving node of receipt of data at the receiving node. This reduces the burden on the system, whilst allowing notification of data transmission over single stages and over the whole transmission path.

IPC Classes  ?

• H04L 1/16 - Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals

Abstract

In one arrangement the data is transmitted from the first transceiving station to the second transceiving station according to a frame structure comprising a payload portion for transmitting payload data and a synchronisation portion for transmitting synchronisation data. The frame structure is selected from candidate frame structures, the candidate frame structures having differing durations of the synchronisation portion, according to a data loading factor, the data loading factor depending on the amount of data that is required to be transmitted. Thus in embodiments of the invention the payload capacity may be optimised by reducing the duration of the synchronisation portion when a large amount of data is required to be transmitted.

IPC Classes  ?

• H04B 7/26 - Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile

Abstract

Embodiments of the invention relate to electronically steered radar systems such as frequency scanning radars that 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. With traditional radar systems that are adapted to provide crawler detection, measurements from successive scans of a given section are compared with one another, and a crawler moving into or out of a specific range cell at a particular bearing can be detected from a change in reflected energy between scans. A problem that is particular to detection of such targets is presented by 'clutter' in the form of grass, bushes, trees etc: the radar tends to see a considerably larger background clutter return, which makes it difficult, if not impossible, to distinguish the crawler from the clutter. A radar system according to an embodiment of the invention comprises 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. Since embodiments of the invention utilise electronically steered antennas, the antenna stares at, rather than glides past, the target and 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.

IPC Classes  ?

• G01S 13/536 - Discriminating between fixed and moving objects or between objects moving at different speeds using transmission of continuous unmodulated waves, amplitude-, frequency-, or phase-modulated waves
• G01S 13/538 - Discriminating between fixed and moving objects or between objects moving at different speeds eliminating objects that have not moved between successive antenna scans, e.g. area MTi
• G01S 7/292 - Extracting wanted echo-signals

Abstract

Embodiments of the invention are concerned with a system for digital communications, and are particularly suited for use in narrowband RF systems. In an RF system data are transceived between radio stations in frames comprising slots having finite periods (and thus discrete start and end points within the frame), and the timing of a clock internal to a given station determines where in time respective slots start and finish. In one arrangement the synchronisation between two communicating radio stations (first and second stations) is configured on the basis of timing information derived from a preamble portion of a given frame that is transmitted from a first station to a second. This timing information is used to configure a clock internal to the second station; by adjusting the time of the clock, the timing of the slots within a given frame can therefore be controlled. This can be particularly advantageously applied to the uplink slots of the given frame (i.e. when the second base station transmits its data to the first station) so as to ensure that data received on the uplink are synchronised with timing characteristics of the first (data processing) station. In embodiments of the invention the data transmitted from the first station is transmitted at a first data rate, the data transmitted from the second station is transmitted at a second data rate, and 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.

IPC Classes  ?

• H04L 7/04 - Speed or phase control by synchronisation signals

Abstract

Embodiments of the invention relate to RF receiver technology and are particularly concerned with aspects of decoding data received at low data rates. In one arrangement, 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. The sequences of data can be embodied as a repeating pattern comprising at least two elements, e.g. first sequence can comprise 24 pairs of {1, 0} 'dotting' and the second sequence can comprise 8 pairs of {0, 1} 'anti- dotting'. This transposition, or interface, between the first and second sequences is identified by components of the signal processor, and enables the receiver to identify bit timing associated with the preamble.

IPC Classes  ?

• H04L 7/04 - Speed or phase control by synchronisation signals