Abstract: An object ranging system operates by transmitting pulses derived from a frequency-swept signal and determining the beat frequency of a combination of the frequency-swept signal and its reflection from an object. A second (or higher) order harmonic is derived from the combination signal. Accordingly, determination of the beat frequency, and hence object range, is significantly enhanced. The frequency sweep is such that frequency changes occur at a substantially higher rate at the beginning of each the pulse repetition interval than at the end. Accordingly, because the frequency changes are concentrated in the period of pulse transmission, even reflections 'from a close object, where the time delay between the source signal and the reflection is very short, will cause a high beat frequency.

Abstract: An object ranging system operates by transmitting pulses derived from a frequency-swept signal and determining the beat frequency of a combination of the frequency-swept signal and its reflection from an object. A second (or higher) order harmonic is derived from the combination signal. Accordingly, determination of the beat frequency, and hence object range, is significantly enhanced. The frequency sweep is such that frequency changes occur at a substantially higher rate at the beginning of each the pulse repetition interval than at the end. Accordingly, because the frequency changes are concentrated in the period of pulse transmission, even reflections ‘from a close object, where the time delay between the source signal and the reflection is very short, will cause a high beat frequency.

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: 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 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 time delay measurement apparatus for determining the delay between two signals comprises a variable delay circuit followed by a processing circuit. The processing circuit extracts events from one of the signals and uses it to sample the other signal. The samples are combined, e.g. by summing or averaging, to determine a value representing the degree of coincidence of the two signals. The operation is repeated for different values of the variable delay in order to determine the delay associated with the greatest degree of coincidence. The processing circuit preferably operates digitally by using gates to cause a counter to have its value changed in a first sense if binary transitions of the two signals occur substantially simultaneously and are of the same type, and in a second sense if the transitions occur substantially simultaneously and are of opposite types. Multiple processing circuits operating on different delays can be provided instead of using the variable delay circuit.

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: 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 therefrom 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: 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 method of classifying an image, in particular the texture of an image, involves first deriving a feature vector representing the texture by mapping a two-dimensional representation of the image into a one-dimensional representation using a predetermined mapping function, and then determining (i) the rate at which the level of the representation crosses a threshold, (ii) the rate at which the level changes when a threshold is crossed, and (iii) the average duration for which the level remains above (or