Abstract: A Doppler sensor operates by transmitting pulses at non-uniform intervals. Samples reflected by an object are processed by multiplying each one by first and second coefficients cxk and sxk, the products being separately summed to form two measures which are examined to determine whether an object exhibiting a particular Doppler frequency fx has been detected. The samples occur at non-uniformly spaced times txk such that the average of a cosine wave of frequency fx sampled at said times txk would be substantially zero and the average of a sine wave of frequency fx sampled at said times txk would be substantially zero.

Abstract: An object is detected by generating a binary signal having an irregular sequence of states and in which transitions between states occur at varying time offsets with respect to a nominal regular clock. The binary signal is transmitted, and a reflection of the transmitted signal is processed with a reference version of the binary signal. The reference signal is delayed, and then used to sample the reflected signal. The samples are used to derive a combined value representing the average time derivative of the reflected signal at locations within the reflected signal which substantially correspond to the times of the transitions in the reference signal. The presence of an object at a range corresponding to the delay is determined from the combined value.

Abstract: An object localizing system comprises sensor devices at different sites, each sensor device being capable of detecting a signal from an object, and control means for repeatedly responding to the outputs of the sensor devices by selecting a sub-set of the devices and determining the amount by which the times at which the devices of the sub-set receive the signal are delayed with respect to each other to enable calculation of the current location of the object. Each sensor device can be switched between a master mode, in which the device is operable to transmit events derived from a signal from an object, and a slave mode, in which the device is responsive to such events from another sensor device for processing its own signal in order to determine the time delay between receipt of the signals by the sensors of the respective devices.

Abstract: A method of determining the location of an object uses data representing the bearing of the object from a plurality of observation locations. The method comprises (a) deriving, for each bearing, the coordinates of a point, the coordinates comprising a first value p representing the signed distance between a predetermined location and the closest point on the bearing line, and a second value ? representing the angle of the bearing line, using a procedure according to which co-linear bearings of opposite direction have first values which are of opposite sign to each other and second values which differ from each other by ?; and (b) deriving parameters defining a curve fitting said points, said parameters representing the object location.

Abstract: An object is detected by generating a m-ary primary signal having an irregular sequence of states. Each transition results in the transmission of a pulse encoded according to the type of transition. Reflected pulses are processed with a delayed, reference version of the primary signal. The presence of an object at a range corresponding to the delay is determined from the extent to which the reflected pulses coincide with transitions in the reference signal. In one aspect, transitions between states of the primary signal occur at varying time offsets with respect to nominal regular clock pulses. In another aspect, the object-detection system is operated while inhibiting the transmission of pulses, and if a significant output is obtained, the parameters of the transmitted signal are altered.

Abstract: The delay between two signals is determined by obtaining zero crossings from each signal, and using each crossing to trigger the sampling of the other signal. Two samples are taken in response to each zero crossing, and the difference between those two samples is calculated. This difference is summed for each event and both signals to derive a value. The process is repeated for different delays between the first and second signals. The values are examined to determine the delay which corresponds to the greatest coincidence between the signals.

Abstract: A wideband irregular signal is decomposed into respective frequency bands, the ratio of the highest to the lowest frequency within each band being in the ratio of approximately 3:1 and the total number of bands being 3 or 4. The wideband signal, or a re-constituted wideband signal formed by combining the decomposed components, is transmitted as a interrogating signal. A reflection of the interrogation signal is decomposed into respective frequency bands, and within each frequency bands the different components are compared. The results of the comparisons are combined to determine whether an object has been detected and, if so, its range. Decomposition of the wideband signal can be achieved by using a bank of low-pass filters in respective frequency bands, the output of each low-pass filter having subtracted there from the output from the filter with the next-lower frequency cut-off characteristic. Delay circuits are used within each channel so that the total delays in each individual channel are equal.

Abstract: Candidate moments within a pulse train are selected. For each such moment, it is determined whether pulses occur at uniform intervals both before and after the moment; if so, the relevant pulses are classified as belonging to a particular group. An accurate calculation of interpulse interval is carried out by working out the repetition interval from the times of arrival of the pulses relative to the candidate moment, and then taking a weighted angular average.

Abstract: A one-dimensional representation of an image is obtained using a mapping function defining a closed scanning curve. The function is decomposed into component signals which represent different parts of the bandwidth of the representation using bi-directional filters to achieve zero group delay.

Abstract: A sequence of waveforms is generated by producing a primary symbol sequence and, for each symbol within the sequence, substituting a randomly-selected waveform. The primary symbol sequence has a narrow autocorrelation function, and may be a train of pulses, with the pulses arranged in packets of predetermined configuration. Objects can be detected by transmitting the waveforms, forming a representation of the transmitted waveform and delaying that representation, and correlating the representation with signals received as a result of reflection of the transmitted waveforms.

Abstract: An entity is subjected to an interrogating signal, and the reflection from the entity is repeatedly sampled to obtain a first set of values each dependent on the intensity of the reflected signal. A logarithmic transformation is applied to the sample values to obtain a second set of values. A set of descriptor values is derived, the set comprising at least a first descriptor value (L) representing the difference between the mean and the median of the second set of values, and a second descriptor value (D) representing the mean of the absolute value of the deviation between each second set value and an average of the second set of values.

Abstract: A method of determining the delay between two corresponding noise-like signals comprises determining events at which the level of a first of the signal crosses a predetermined threshold, using each event to sample a second signal, combining the samples to produce an output value and determining the delay from the output value. Preferably, each sample is weighted according to one or more characteristics of the event used to define the sample. The magnitude of the output value could be an indication of the delay, or there could be several output values each for a respective differently-delayed version of the second signal, in which case these could be evaluated to select which corresponds to the actual delay.

Abstract: A pulse sequence is produced by repeatedly selecting individual pulse trains at random from a set thereof, each pulse train meeting predetermined autocorrelation constraints and the pulse trains collectively meeting predetermined cross-correlation constraints. The pulse trains are preferably separated by gaps of random length. At least some pulse trains may be time-reverse replicas of others. The resulting sequences are particularly suitable for obstacle detection in multiuser environments.

Abstract: An object localising system comprises sensor devices at different sites, each sensor device being capable of detecting a signal from an object, and control means for repeatedly responding to the outputs of the sensor devices by selecting a sub-set of the devices and determining the amount by which the times at which the devices of the sub-set receive the signal are delayed with respect to each other to enable calculation of the current location of the object. Each sensor device can be switched between a master mode, in which the device is operable to transmit events derived from a signal from an object, and a slave mode, in which the device is responsive to such events from another sensor device for processing its own signal in order to determine the time delay between receipt of the signals by the sensors of the respective devices.

Abstract: A transmitted signal and a received signal are combined and the combination is expected to determine whether or not a target signal is present. Either the transmitted signal or the received signal is combined with an auxiliary signal containing a range of frequencies corresponding to an anticipated Doppler shift, so that an output of the combined transmitted and received signal will be present only if a target signal exhibiting a Doppler shift within the anticipated range is present. The auxiliary signal preferably comprises finite-duration signal portions of different types so as to provide a substantially uniform frequency response throughout the selected range.

Abstract: A random binary signal is generated using a plurality of noise sources, each of which defines events occurring at random intervals, the outputs of the sources being combined in such a way that the events are interspersed in the resultant signal.

Abstract: A time measurement system for measuring the delay between first and second signals comprises means for detecting the times of upcrossings when the first signal crosses a predetermined level (preferably substantially different from the average level) with a positive slope and the times of downcrossings when the first signal crosses the predetermined level with a negative slope. These events are transmitted to a remote device receiving the second signal, which uses the events to define respective staggered segments of the second signal, to sum said segments and to detect a predetermined feature in said sum, the position of said feature representing the delay between the first and second signals.

Abstract: A signal can be analysed to determine statistical characteristics indicative of, for example, the predictability or time reversibility of the signal. The signal is examined to locate events corresponding to the crossing of predetermined levels with predetermined slopes. Multiple versions of the signal are combined, the versions being shifted with respect to each other by amounts corresponding to the spacings of the detected events. The shape of the resulting representation provides statistical information regarding the signal.

Abstract: An object localising system comprises sensor devices at different sites, each sensor device being capable of detecting a signal from an object, and control means for repeatedly responding to the outputs of the sensor devices by selecting a sub-set of the devices and determining the amount by which the times at which the devices of the sub-set receive the signal are delayed with respect to each other to enable calculation of the current location of the object. Each sensor device can be switched between a master mode, in which the device is operable to transmit events derived from a signal from an object, and a slave mode, in which the device is responsive to such events from another sensor device for processing its own signal in order to determine the time delay between receipt of the signals by the sensors of the respective devices.

Abstract: A time measurement system for measuring the delay between first and second signals comprises means for detecting the times of upcrossings when the first signal crosses a predetermined level (preferably substantially different from the average level) with a positive slope and the times of downcrossings when the first signal crosses the predetermined level with a negative slope. These events are transmitted to a remote device receiving the second signal, which uses the events to define respective staggered segments of the second signal, to sum said segments and to detect a predetermined feature in said sum, the position of said feature representing the delay between the first and second signals.