Abstract: In a cellular radio system having a two layer cell structure comprised by macrocells (1) overlaying microcells (2), handover occurs only via the macrocell layer. Thus when the quality of a call handled by a microcell (2) deteriorates below predetermined criteria the call is handed up rapidly to the umbrella macrocell and is only handed back down to a microcell when the handset has been in that microcell for a predetermined time and the quality of the link thereto exceeds predefined criteria.

Abstract: In a cellular radio system including a plurality of cells (e.g. cell sectors or micro cells) (4, 5, 8, 9, 10, 11) each normally using a respective channel for interference reduction purposes, a number of the cells are arranged in groups (6) and in the event of a cell associated with equipment moving within a group (6), all cells (4, 5, 8, 9, 10, 11) of that group use a common channel whereby to facilitate handover between them.

Abstract: A first (receiver), for example, pseudo random binary sequence (PRBS) generator (6) is synchronized with a second identical PRBS generator (2) at a tramsitter by adding a PRBS (u(x)) to a data stream (w(x)). The data stream includes a known value at periodic intervals. The received data is framed (5) and thus the position of the known data values determined. The received data is sampled at these positions to produce a sequence of samples (s(x)) comprising a sampled version of the transmitter PRBS. The phase of the transmitter generator (2) is determined for the samples and the phase of the receiver generator (6) adjusted to correspond. (FIG. 1). Implementation with sequence generators other than binary sequence generators are also discussed.

Abstract: A communication procedure suitable for a cordless telephone system involves time division duplex radio communication between a handset 11 and a base station using alternating bursts of transmission over a single radio channel. Once a radio link has been set up, initial transmissions carry a synchronization logical channel S and a signalling logical channel D multiplexed together, but the link may switch to bursts carrying a communications logical channel B for the speech data and the signalling logical channel D. Burst synchronization is achieved by the asynchronous detection of words in a synchronization channel S. These words have bit patterns reducing the probability of incorrect asynchronous detection of them. If one part ceases to receive handset signals from the other, it transmits a special signal, informing the other part. This enables both parts to detect the failure of a link at substantially the same time, so that their actions to re-establish the link are synchronized.

Abstract: A holographic optical correlator includes a matched optical filter and control means therefor including a memory. In use searching for occurrences of an item to be found is carried out by the control means controlling the input and Fourier transform planes of the filter and a coherent light source for parallel optical processing of the memory content and the output plane of the filter provides information to the control means as to the location in the memory of occurrences of said item. The complexity of the detector means in the output plane can be reduced in comparison with previous proposals by moving the item to be sought step-wise across the input plane. The detector means then may comprise a single column of detectors which are required to detect a peak correlation signal within a predetermined range.

Abstract: A neural plane, which can form the basis of a neural network or a component thereof, is comprised by an optical modulator, an electrical non-linearity circuit and an optical detector interconnected whereby in use the non-linearity circuit controls the modulator in dependence on the detector output. There are parallel arrays (10, 11, 12) of such modulators, non-linearity circuits and detectors (M, T, D, 30, 33, 34). The modulator, non-linearity circuits and detectors have components formed in a common semiconductor substrate (20), for example by VLSI techniques with a silicon substrate, the modulators (30) may be comprised by liquid crystal on silicon in that case (FIGS. 4, 7).

Abstract: A communication procedure suitable for a cordless telephone system involves time division duplex radio communication between a handset 11 and a base station 3 using alternating bursts of transmission over a single radio channel. Once a radio link has been set up, initial transmissions carry a synchronization logical channel S and a signalling logical channel D multiple together, bu the link may switch to bursts carrying a communications logical channel B for the speech data and the signalling logical channel D. Bursts synchronization is achieved by the asynchronous detection of words in a synchronization channel S. These words have bit patterns reducing the probability of incorrect asynchronous detection thereof. If one part ceases to receive handset signals from the other, it transmits a special signal to inform the other part. This enables both parts to detect the failure of a link at substantially the same time, so that their actions to reestablish the link are synchronized.

Abstract: Soliton-type interaction is eliminated in optical fibre communications system by making the fibre appear to be a passive optical pipe to a signal to be transmitted along it. In particular, the signal to be transmitted is intensity modulated and at a first wavelength which is greater than the minimum dispersion wavelength of the fibre by a predetermined amount. This signal is launched simultaneously into the fibre with a signal of dark pulses of the same format but at a wavelength less than the minimum dispersion wavelength by the predetermined amount. As a result the light transmitted in the fibre is of constant intensity and soliton-type effects, which rely on intensity variation for their formation, do not occur.

Abstract: An automatic telephone system enabling subscribers access to more than one network (3,4). The subscriber's line (2) accesses the networks (3,4) via a highway providing at least two traffic channels (B) and one signalling channel (D). The signalling channel (D) conveys call setting and other signalling for calls set up via any traffic channel (B). Access of a particular traffic signal channel to a particular network is provided by an intelligent multiplexer/concentrater (1) in response to a network identifier carried by the signalling channel, for example an appropriate value of a SAPI (Service Access Point Identifier) in the case of an ISDN I-Series signalling system.

Abstract: A method of installing a cable, particularly but not exclusively in a duct filled with flowing liquid, wherein, as the cable is deployed, the strain in the cable is determined by sending a signal down the cable and receiving a signal back from the cable. The speed of deployment is adjusted according to the strain detected. Preferably the system is applied to optical cables, and a radio frequency signal is modulated on an optical carrier. Optical connection to the cable on the rotating drum is made via an optical slip-ring. The front end of the cable has a silvered end termination for reflecting the modulated signal back along the fibre to be detected by an optical receiver, and there is a vector voltmeter for determining the phased difference between the signals to thus determine the strain in the cable.

Abstract: A broadcast facility is provided in a synchronous network comprising a number of nodes (b 20l ) coupled via a star coupler (b 21l ). Data is transmitted via the network in a sequence of frames. Each node with a public write to send transmits it to all system nodes (including itself) in the next available frame. Each node has its own identifying characteristic, e.g. a unique assigned frequency. These identifying characteristics determine the notional order in which data packets within a frame are received thus providing each frame with a timestamp.

Abstract: Apparatus for synthesizing complex composite RF signals comprising a source of unmodulated RF carrier signal, means for splitting the RF carrier signal output of the source into equal components, separate modulating means to which respective carrier signal components are applied, signal combining means to which the outputs of the modulating means are applied, and separate computerized in-phase and quadrature baseband control signal generating means the outputs of which are applied to respective modulating means to effect modulation of the respective carrier signal components.

Abstract: Relaxation effects of a uniform mode ferroelectric liquid crystal cell with obliquely evaporated alignment layers, characterized by the reduction in apparent tilt angle consequent upon removal of a switching stimulus, are eliminated by a poling treatment that typically comprises the application of a relatively low frequency (c. 500 Hz) relatively large amplitude (c. 60 volts peak-to-peak) electric potential difference across the thickness of the liquid crystal layer.

Abstract: Cable deployment in a fluid filled pipeline under pressure is monitored by use of a strain gauge device coupled between the leading end of the cable and a drogue. The strain gauge measures the pull of the drogue on the leading end of the cable and the strain gauge signal is transmitted back to the other end of the cable via the cable conductors. Changes in fluid flow rate, features of the pipeline, and failure of the drogue to inflate can be detected quickly by monitoring the strain gauge signal, so that the cable feed rate can be changed accordingly in order to maintain satisfactory deployment.

Abstract: The gain of an optical amplifier is maintained constant by employing a portion of the amplified optical signal in a feedback loop. In one arrangement this is used to control the output of a pump signal source accordingly. The portion of the said signal corresponds to spontaneous emission (ASE) at a control wavelength or band of wavelengths different to the wavelength of the optical signal output. In the case of an erbium, for example, optical fibre amplifier the portion is preferably ASE at 980 nm, the amplified signal being at 1.535 .mu.m, i.e. completely different transitions in the amplifying medium are used for gain and ASE feedback in order to lessen requirements on the filter used to extract the portion for the feedback loop.

Abstract: A fact acting automatic gain control system comprising a single or serial multistage arrangement. In one multistage embodiment (FIG. 1) each stage (13) has a first state with a predetermined gain and a second state with unity gain. The output of each stage determines what state is finally adopted although initially when a signal is input it is in the first state due to the action of a sequence controller (14). The predetermined gain values may comprise a binary sequence which descends in the direction towards the output. If the level detector (7) threshold is exceeded, the stage is set to the second state. A particular use of the system is to ensure burst mode pulses reaching a receiver are of similar amplitude. A similar arrangement can be employed for phase alignment ratther than gain control. In another multistage embodiment (FIG.

Abstract: A switchable multichannel external cavity injection laser incorporates a diffraction grating between a linear array of n reflectors and a common reflector to define a set of n optical cavities having different frequency bands. Each of the (n+1) reflectors is provided by the optically distal end of an associated semiconductor laser amplifier whose optically proximal end is arranged to be substantially non-reflective.

Abstract: An optical receiver incorporating a voltage dependant impedance arranged to shunt excess AC photodetector signal away from the receiver amplifier in response to light level.

Abstract: A flexible termination between a submersible repeater housing and a submarine cable comprises a double ball link bar (20) and a cooperating socket (12) coupled to the repeater housing (1) and a similar socket (11) coupled to the cable. This enables a compact lightweight flexible termination having a large angle of flexure. In an alternative embodiment a double gimbal arrangement is used.

Abstract: An aerial optical fiber cable comprises a glass-fibre-reinforced plastics core member (1) having a slot (2) with a zero lay angle accommodating loose-tubed optical fibres (3, 3A) and sheathed with a longitudinal tape (13) bound with a binder (915) and over-sheathed with a plastics extrusion (14). The cable is self-supporting and completely non-metallic and ia suitable for telecommunications and data transmission services alongside overhead power transmission systems. An alternative embodiment (FIG. 2 ) is not self-supporting but is similar in design and adapted for support from a support wire, and another embodiment has a rectangular slot housing one or more ribbon elements. The cable is simple and cheap to make.