Nortel Networks Corporation

Itt Industries, Inc.

Northern Telecom Limited

International Telephone and Telegraph Corporation

Stc, Inc

Roger J Williamson

Gillies D Pitt

Christopher Neville Tate

Leslie Derek Humphrey

David N Batchelder

Igor Kajetan Czajkowski

Michael F Grant

Andrew David Wallace

Mark Bridger

Arulanandam M Prabakaran

Rudolf A Heinecke

Bryan Parlor

Jeffrey Farrington

Jonathan Beattie

To facilitate acquisition of lock in a multiple sub-channel carrier scheme, a plurality of time-continuous pilots ( ) on known sub-channels are made available to an addressed unit across the frequency spectrum. The addressed unit is then able to select one of these pilots for training purposes and specifically for frequency and phase acquisition ( ). The selection is based, typically, on the pilot with either the best signal to noise ratio or the first pilot to satisfy the minimum quality requirements for effective training. Discontinuous carriers, of which there can be several, are then used to identify a symbol boundary at the addressed unit. Once acquisition has been established, the pilots can, if desired, be released to carry low-bit rate traffic, although it is preferable to retain pilot tones for use within the system. Selection of the pilot from one of a number of alternative sub-channels distributed through the spectrum therefore ensures accurate synchronisation irrespective of whether portions of the spectrum are generally noisy and unclean.

Method of setting-up and controlling synchronization within a modem

A method of and apparatus for capacity determination in a telecommunications system, in the presence of Gaussian and non-Gaussian noise. The ratio of Gaussian to non-Gaussian noise is determined utilising a statistical metric. Preferably the metric is Kurtosis or the 3 Cumulant of the Probability Density of the signal at each frequency. The determination of the ratio of Gaussian to non-Gaussian noise enables a more accurate determination of Noise, which in turn allows greater utilisation of actual available capacity in the system.

Method of and apparatus for determining the capacity of a telecommunications system

A subscriber's telephone installation comprises a plurality of telephone sets coupled in parallel to a subscriber loop so as to provide a voice facility, and a data modern coupled to the subscriber loop so as to provide data facilities at a frequency above that employed for said voice facility. Some or preferably all telephone sets are provided with a respective filter arrangement incorporating series connected inductive and parallel connected capacitive elements for rejecting selected frequencies from the telephone set. The filter also incorporates a switch responsive to current drawn from the line for selectively enabling and disabling the filter arrangement when the telephone set is respectively in its off-hook condition or in its on-hook condition.

Telephone filter arrangement

A splitter separates telephony traffic (POTS) from digital subscriber line (ADSL) traffic occupying a higher frequency band. The splitter comprises a low-pass filter for passing the telephony traffic, the low-pass filter being operable to vary its filtering response between a first low-pass response for use during telephony speech traffic, and a second, more restrictive, low-pass response for use during at least part of the time that telephony signalling traffic is present. During speech traffic a filter is used which provides a good impedance match with a telephony terminal or linecard so as to minimize detrimental effects on sidetone and echo performance which may impair a user's speech quality. The filter response can be varied according to a detected property of the telephony traffic, such as amplitude or rate of change of amplitude of the traffic.

Communications signal splitter and filter

Customer premises equipment for a telecommunications DSL subscriber is adapted to provide a lifeline voice service under a fault condition, e.g. a power failure at the subscriber station. The arrangement incorporates a number of switchable local subscriber ports each providing access to a respective telephone instrument, and a router circuit whereby, under normal conditions, voice calls may be routed each to a respective loop port. Under a fault condition the router directs an incoming call to a selected port to provide the lifeline service. Further calls may be barred when such a lifeline call is in progress.

Voice over digital subscriber line call redirection for lifeline service

To facilitate the use of relatively high frequency data transmission services over a wireline communication resource originally deployed to support low frequency voice band services, an assessment of the wireline communication resource ( - ) is based on attenuation of high frequency test signals, of known original level, that are generated ( ) injected into the wireline communication resource from a test point ( ). A detector ( ) at a potential point of service, e.g. at a customers' premises ( ), detects an attenuated level of the test signals and generates a control signal ( ), such as a drive current, indicative of the attenuation caused by the wireline communication resource ( - ). The control signal ( ) is then indirectly communicated back to the test point ( ) in a coded form, and preferably within a voice band transmission. The coded form may be realized as modulation of a power supply provided to the customers' premises by the wireline communication resource, or could be achieved by up-link frequency mixing. In its most basic form, the control signal causes fluctuation on a visual level indicator at the customers' premises and therefore relies on a customer providing a verbal or toned response to the test point as to the level of the visual indicator. Effective attenuation at high frequencies can then be assessed based upon analysis of information coded into the voice band signal and its direct relationship with the original level of the injected high frequency signals.

Line testing method and apparatus therefor

A method, apparatus, and software for providing lifeline service during power failure affecting Customer Premises Equipment (CPE) in a Digital Subscriber Loop (DSL) arranged to carry voice traffic in band rather than on a separate analogue POTS band. The arrangement provides a reduced service, capable of supporting at least one voice call, to operate during such power failure and, where a single call is in progress during power failure, that call may be maintained during the transition from DSL to analogue POTS lifeline service. Where a call is in progress upon power restoration, the lifeline POTS service may be maintained until completion of the call so as not to interrupt a potential lifeline call.

Lifeline telephony provision for voice over digital subscriber line

To avoid spurious energy radiation from a wireline communication resource (42-44) supporting data over voice, such as in xDSL, modems (40, 46) supporting a multi-carrier transmission scheme undertake a line balance assessment (136-138) for each sub-channel carrier within the system. Specifically, an addressed modem (40) measures, for example, the signal to noise ratio of a differential transmission mode and a common transmission mode to provide the balance assessment (138). More particularly, a receive chain in the addressed modem is selectively switched (84) to receive the differential mode as appearing across the terminals of an isolation transformer (66) or the common mode (as seen with respect to ground) from a center tap (88) in a line-side winding (70) of the isolation transformer (66). Any sub-channel carrier that fails to provide a predetermined level of balance (140) is de-selected (141) by the modem and not used for traffic. Generally, the modems (40, 46) at both ends of the wire-line connection (42-44) notify one another of selected sub-channels, while the concept can be employed in a dynamic in-call fashion (152, 158-160).

Wireline modem, communication system and method of setting-up such

A resonator comprises a quartz resonator element (11) sealed between a pair of flat quartz housing members (12, 13) the resonator comprises an active central region 110 defined by an annular recess 111 within which vibrational energy is trapped. The crystal orientation of the housing may be aligned with that of the resonator to minimise thermal effects.

Crystal resonator device

The method of measuring a resonator such as a quartz crystal is to calculate its admittance from the voltage transfer function of a suitable network incorporating the resonator. This admittance can be expressed in the form of a circle. Two initial measurements are taken from which an approximate circle is calculated. This circle is used to calculate the optimum measurement positions for the subsequent curve fitting routines, those positions being symmetrically placed around the series resonance. Each measurement is an average of a number of samples. The deviation from this average as well as the deviation from the circle defined by previous measurements is used to monitor the measurement. All the parameters are calculated by least square curve fitting of the first the admittance circle and then the variation of phase around the circle with frequency.

Method of measuring the parameters of a resonator

In order to determine the vortex shedding frequency, from which the fluid flow rate may be calculated, an optical beam, such as produced by a laser, is passed through a fluid, transversely to a vortex street therein, and modulated in dependence on the alternate high and low velocity regions comprising the vortex street. The modulated signal is detected and 'cleaned' of noise by filtering with a first (high) band-pass filter of a center frequency f.sub.c, such that the first filter output comprises an amplitude modulated signal of carrier frequency f.sub.c modulated by the vortex shedding frequency, that is the frequency of oscillation of the power spectra between the respective curves for the high and low velocity regions. The first filter output is demodulated and filtered by a second (low) band-pass filter, whose output is of a frequency comprising the vortex shedding frequency.

Vortex shedding fluid flowmeter

A vortex flowmeter having a double bluff body arrangement whereby vortices are generated at a rate corresponding to the fluid flow velocity. The upstream body and the downstream body together interact with the fluid stream to generate vortices. The arrangement introduces a relatively low blocking factor in comparison to simple bluff body arrangements. Vortex sensors are located between the bodies and downstream of the second body a distance between three and five times the diameter of that body.

Fluid flowmeter

A bluff body is placed in a fluid pipe with one flat face facing the oncoming fluid. Vortices are then generated and shed alternately from opposite edges of the body. This body is of a scalene triangle cross section, and in one version a hole extends transversely therethrough. A longitudinal hole intersects the first hole at right angles thereto. The vortices cause oscillations in the transverse hole. A light beam is provided in the longitudinal hole. The light beam is modulated as it crosses the path of the transverse hole. Hence by measuring the frequency at which the beam is modulated and by suitable calibration, one gets a good and reliable indication of fluid flow rate. In a second version the transverse hole is formed into a blind hole at the foot of which is an etalon (a Fabry-Perot interferometer). The effect of the fluid oscillations due to vortex generation influences the etalon so that its output is a measure of the fluid flow rate.

Vortex flowmeter

A fluid flowmeter of the vortex shedding type. The vortex frequency is determined from variations in the internal reflectivity of a prism 16 mounted in the fluid and coupled to a light source 13 and to a detector/frequency meter 14 via an optical waveguide arrangement 15. Passage of a vortex adjacent the prism 16 causes a temporary change in the local fluid refractive index and hence a change in the intensity of light internally reflected by the prism.

Apparatus for measuring fluid flow

An optical fibre strain gauge arrangement is employed to take advantage of a so-called speckle effect. As used in a simple strain gauge, a coherent light source, e.g. a laser, launches light via a suitable launching device into a multimode optical fibre or fibre bundle. Due to slight differences in transmission times in the fibre or fibre bundle the light as received at a detector has a speckle pattern. If the fibre or fibre bundle is subjected to strain, the various transmission times are caused to change so that the speckle pattern shifts, the amount of the shift being a measure of the strain. This principle is usable in a vortex flowmeter where the vortices produced by a bluff body influence such a fibre arrangement. Further, when used underwater, passing ships and submarines may be detected. In a building, the arrangement may be used as an intruder detection system.

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Harlow, United Kingdom

Roger J Williamson