Abstract: In a multilateration system receivers are grouped into two groups. The first group is used to determine a position of a signal source, for example, an aircraft equipped with a SAR transponder. From the determined position, predicted time of arrival values are produced for the second group receivers. These are compared with the actual time of arrival values for the signals arriving at the second group receivers. A difference is determined and then the variation of that difference is determined as the aircraft travels in its track. The groupings are then varied and further variations determined. When the minimum variation is determined an alert is given that the second group has a receiver which is operating with a larger than desirable group time delay.

Abstract: The Video Motion Anomaly Detector addresses the problem of automatically detecting events of interest to operators of CCTV systems used in security, transport and other applications, processing CCTV images. The detector may be used in a number of ways, for example to raise an alarm, summoning a human operator to view video data, or to trigger selective recording of video data or to insert an index mark in recordings of video data.

Abstract: A method of controlling interference from a transmitter (4) in one communication system to a receiver (1) in another communication system, the method comprising transmitting a beacon (3) beacon from a beacon transmitter associated with the receiver representative of a frequency at which the receiver is trying to receive; listening for the beacon at a beacon receiver associated with the transmitter; and deriving a power spectral density limit for a transmission (2) from the transmitter based upon the strength of the beacon received at the beacon receiver.

Abstract: To cater for the positioning of an aircraft in a boundary zone between two adjacent multilateration systems, the controller (14) in one system receives Time Difference of Arrival data provided by the controller (15) in the second system. The controller (15) derives the TDoA data from time of arrival data provided by its receiver stations (9-13). By furnishing TDoA data the timings of the two systems do not need to be synchronised. The controller (14) uses the TDoA data and also time of arrival data from its local receiver stations (4-8) to perform a multilateration to determine the location of the aircraft (16).

Abstract: In a method for downloading software from a mobile network operator to a mobile phone user, the downloaded software can be new network services or user specified applications software or user specified information, written as Java classes capable of running on a Java Virtual Machine. All the Java classes can be continuously broadcast at a relatively modest data rate. In an enhanced mode a list of services available for downloading is broadcast over the network more frequently then the actual services themselves. The user then selects which service he wants, and only that one is downloaded. Payment can be 100 on a subscription or pay-per-use basis. The method could also be adapted to work with one of the new digital broadcasting platforms such as DAB or DVB as a means for delivering the Java classes.

Abstract: A method of processing an encoded data stream comprises determining one or more data strings of interest; wherein the data string comprises a predetermined sequence of characters; encoding (3) the or each data string using the same encoding that was used to encode to the data stream; and searching (4) for the encoded data string in the encoded data stream.

Abstract: In a method of constructing an Aho-Corasick tree, tree is constructed in a general depth first manner, one string at a time. Preferably during the construction of the string, after each node is added, failure links or extended failure links from that node to other nodes are added and failure links to nodes in the newly inserted branch are re-updated.

Abstract: A method of transmission comprises receiving at a first destination, a transmission from a first source; determining from the transmission from the first source, the maximum permitted additional interference subject to which the first destination can still communicate; sending an acknowledgement of the transmission and including in the acknowledgement an indication of the determined maximum permitted additional interference. A second source determines whether it has received the transmission from the first source, or the acknowledgement from the first destination, at a power level lower than that of the maximum permitted additional interference given in the indication; and if so, the second source sends a transmission to a second destination, which at least partially overlaps in time, communication between the first source and first destination.

Abstract: To gain visiting access to a wireless local area network (W-LAN), the operator of which administers a visitor authentication, authorization and accounting (VAAA) server, a user requesting such access must have a valid cellular mobile account, a portable computing device with a browser and a valid W-LAN card from another operation that administers a home authentication, authorization and accounting (HAAA) server. The user, inputs, via the VAAA server, identity information that enables the HAAA to issue a personal identification number (PIN) which is encoded and forwarded to the user's mobile telephone. This encoded PIN is transferred to the browser to authenticate the requested visiting access, and the costs of such access are billed to the user's cellular mobile account. The requested access is achieved via the user's browser. The user may employ the browser to convey the identity information, to the VAAA via the W-LAN, or via the mobile telephone.

Abstract: Radio wave detection apparatus includes an array of antenna elements which are able to receive radio waves which enter and leave the array. In this way antenna elements are able to cater for the detection of different types of polarisation from the one configuration.

Abstract: In the described system the multilateration process to be applied to determine an aircraft's position is chosen on the basis of the available returns, receiver geometry and the height of the aircraft.

Abstract: A ground plane for an antenna comprises first and second planar conductors (102, 103) arranged substantially perpendicular to a central axis of the antenna joined together and spaced from one another by a third conductor (104) arranged substantially concentric with and parallel to the central axis. An edge of the first planar conductor (102) is radially outward of an edge of the second planar conductor (103), and the second planar conductor extends radially outwardly from the third conductor (104) a distance of substantially one sixth of a wavelength of an operating frequency of the antenna.

Abstract: Routers for trunk telecommunication systems currently operate at 2.5 Gb/s. Next generation routers will be required to switch 128 input data streams into 128 output data streams, each data stream being at a data rate of 10 Gb/s. Current routers employ massively parallel electronic switches to route data at 1.25 Gb/s. Such technology is reaching its limit and a new approach to high-speed switching is required. The present invention provides an apparatus and method for enabling such high-speed switching by providing a data compression apparatus which comprises a pulsed chirped laser (226) coupled to a modulator (218, 220), the modulator (218, 220) being coupled to a compressor (228, 230). A chirped laser pulse having the duration of a data packet is modulated with data received on an input channel and then passed through the compressor (228, 230) in order to generate a compressed modulated data pulse for high speed switching.

Abstract: A method of filtering sections of a data stream involves determining a set of characters of interest, testing each section of the data stream for the presence of one or more of the set of characters of interest and extracting sections in which at least one of the characters is present.

Abstract: In a multilateration apparatus a correlator is provided with a time of arrival correlation window which is set to cater for the path lengths that may be experienced before a signal from an object to be located is received by receivers in the system. This may be on the basis of the largest possible path length in the system or on a receiver by receiver basis.

Abstract: A method of extracting sections of a data stream, the sections including a set of sequences. Each sequence is encoded separately and coupled together to define a section. The method involves determining a combination of at least two sequences of the set, comparing the combination of sequences with sequences in the data stream, and rejecting or accepting extraction of the section of the data stream based upon the result of the comparison. If the combination of sequences does not include a start and end marker for the section, a search for the start and end markers is carried out before the section is extracted.

Abstract: A method and apparatus are described for the unwrapping of a set of phase values observed for an incoming signal on a phased array antenna. The difference between values observed on adjacent elements in the array forms a first data set. The differences between adjacent ordinates in the first data set forms a second data set. The values in the second data set are rounded to the nearest whole multiple of one complete cycle before the differencing process is reversed to provide the values (representing a whole number of complete cycles) which are added to the observed phase values to provide the unwrapped phase values.

Abstract: An apparatus having a transmitter portion and a receiver portion each isolated from each other and comprising a plurality of antennae, each antenna being selectively connectable to both the receiver portion and transmitter portion, said antennae thus being common to both transmitter and receiver. It may be adapted such that one antenna is selectable to be used as a transmitter whilst at the same time an alternative antenna is selectable to be used as a receiving antenna.

Abstract: A method is provided for controlling a clock for use in a frequency source. In the method a time bias is determined by determining the Accumulated Doppler Range of a signal source at different time intervals. The drift of a local clock is determined by determining the difference between the different time intervals and the clock may then be corrected. Apparatus is also provided and the invention has particular application to a multilateration system.

Abstract: An RFID tag includes a plastic container having at least one particle that is disposed therein and that is formed from metal or metal coated and/or fabricated from a plurality of different metals. A receiver unit detects RF pulses which are generated by the Triboelectric effect of the particles.