WO2006089888A1

WO2006089888A1 - Method and device for evaluating attenuation of signals transmitted, at a predefined frequency, over a copper pair of a local loop

Info

Publication number: WO2006089888A1
Application number: PCT/EP2006/060141
Authority: WO
Inventors: Jean Schmitt; Peter Muggenthaler
Original assignee: Acterna Ipms
Priority date: 2005-02-22
Filing date: 2006-02-21
Publication date: 2006-08-31
Also published as: FR2882477B1; EP1851945A1; FR2882477A1

Abstract

The invention concerns a method and a device for evaluating attenuation of signals transmitted, at a predefined frequency, over a copper pair connecting a user's installation to a local loop. The method includes the following steps: a) detecting the presence on said copper pair of at least one normalized carrier; b) measuring the amplitude of the detected carrier; c) comparing the measured amplitude to a predefined theoretical amplitude for said normalized carrier; d) calculating the attenuation of the detected carrier on the copper pair from step c); e deducing from step d) attenuating, at said particular frequency, the signals transmitted via said copper pair.

Description

METHOD AND DEVICE FOR EVALUATING THE ATTENUATION OF

SIGNALS TRANSMITTED, AT A PREDEFINED FREQUENCY, ON A

PAIR OF COPPER OF A LOCAL LOOP

DESCRIPTION

TECHNICAL AREA

The invention lies in the field of

Telecommunications and concerns the pre-qualification of the local loop (copper pairs) lines used for the transport of xDSL technologies

(ADSL, ADSL2, ADSL2 +, G. SHDSL, VDSL ....).

The invention more specifically relates to a method for evaluating the attenuation, at a given frequency, of the transmitted signals, on a line connecting a user installation to a local loop.

The invention also relates to a device for implementing the method.

STATE OF THE PRIOR ART

The pre-qualification of a copper pair connecting a user installation to a local loop consists of determining the physical parameters of this pair and the disturbances due to its environment in order to evaluate the capacity of transmission of broadband signals. . The maximum throughput that a local loop copper pair can carry is mainly related to its physical parameters (linear capacitance, linear resistance, linear conductance and linear inductance) and its environment (broadband noise levels at each end, crosstalk at each end linked to the proximity of other pairs, impulsive noise ...).

Reliable and accurate knowledge of reference frequency attenuation of xDSL technologies (eg 25 KHz to 1.104 MHz in ADSL) allows telecommunication operators to define the eligibility of a subscriber according to the level of attenuation of his telephone line (copper pair). FIG. 1 schematically illustrates a device for measuring, according to a first method of the prior art, the attenuation on a pair of copper 2 connecting a user installation

(not shown) to the local loop 4 of an operator. In this method, a transmitter / receiver 6 connected to the equipment of the telecommunications center (not shown), measures the noise at this equipment, and a receiver 8, connected to the user installation, measures the noise of the equipment. side of the subscriber. During the measurements, the copper pair 2 is disconnected from the subscriber's installation (telephone set, separating filter, modem or xDSL router ...).

This first method has economic disadvantages because, in addition to the disconnection of the subscriber, it requires the movement and the presence of a technician at each end of the line to qualify.

A second method of the prior art consists in making noise measurements by time domain or frequency domain reflectometry. only on the telecommunications center side. For this purpose, the transmitter / receiver 6 is connected to the telecommunications center and the receiver 8 is connected to the user installation for measuring the bandwidth or the attenuation of the copper pair 2 in the frequency band used. for the required xDSL technology (example from 25 kHz to 1.104 MHz in ADSL).

Unlike the first method, this second method requires the presence of a single technician and does not require the disconnection of the copper pair 2 of the subscriber installation for the duration of the measurement. However, the receiver 8, connected to the subscriber's installation, systematically adjusts the impedance of the line and generates signals to allow the equipment of the telecommunications center to synchronize. The adaptation of the impedance of the line has the effect of greatly reducing the signal reflections necessary to perform reflectometry measurements. In addition, the presence of synchronization signals disturbs the reflectrometers and in most cases renders their results inconsistent or unreadable.

The object of the invention is to overcome the disadvantages of the prior art described above.

More particularly, the object of the invention is to overcome the problems inherent in OTDR methods when an active device of the modem or DSL router type (called HTU-R in the international IUT-T or ETSI specifications) is connected to the OTDR. end of the copper pair on the subscriber side. I / INVENTION STATEMENT

The invention recommends a simplified method enabling operators to determine the attenuation of the signals passing through the copper pair connecting the user installation to the local loop of the operator to the transmission frequencies provided to provide broadband services. through the phone line. More generally, the invention proposes a method of evaluating the attenuation, at a particular frequency, of the signals transmitted on a copper pair connecting a user installation to a local loop. This method comprises the following steps: a) detecting the presence on said copper pair of at least one normalized carrier, b) measuring the amplitude of the detected carrier, c) comparing the measured amplitude with a predefined theoretical amplitude for said standardized carrier, d) calculating the attenuation of the normalized carrier detected on the copper pair from step c); e) deducing from step d) the attenuation, at said particular frequency, of the signals transmitted via said pair of copper.

In a particular application of the invention, the user installation is connected to the local loop by a broadband channel of the DSL type. According to a preferred embodiment of the invention, step e) is carried out on the basis of a predefined attenuation model representative of the local loop of a given operator. In a particular embodiment of the invention, the normalized carrier belongs to one of the following standard types defined by ITU-T G.994.1: A43, B43, C43 or A4.

The invention also relates to a device for evaluating the attenuation, at a particular frequency, of the signals transmitted on a copper pair connecting a user installation to a local loop. This device comprises:

means for detecting the presence on said copper pair of at least one normalized carrier,

means for measuring the amplitude of the detected carrier,

means for comparing the measured amplitude with a predefined theoretical amplitude for said normalized carrier,

means for calculating the attenuation of the detected normalized carrier,

means for deriving attenuation, at said particular frequency, of the signals transmitted via said copper pair from the attenuation of the detected carrier.

The device according to the invention further comprises measuring equipment connected to one end of the copper pair and a DSL modem connected to the user installation. BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will emerge from the description which follows, taken by way of non-limiting example, with reference to the appended figures in which:

FIG. 1, previously described, schematically illustrates a device for measuring attenuation on a copper pair implementing a first method of the prior art; FIG. 2 diagrammatically illustrates a first embodiment of the invention;

FIG. 3 represents an experimental curve illustrating the evolution of the attenuation in a given cable as a function of the frequency of the signals which flow through this cable,

FIG. 4 schematically illustrates a predefined attenuation curve for standard carriers f1, f2, and f3,

FIG. 5 represents an example of a measurement result indicating the evolution of the amplitude of a signal as a function of frequency.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

In the remainder of this description, identical references will be given to the elements common to the prior art and to the invention. We will designate by user installation (CPE, for Customer

Premises Equipment) a private network for connecting one or more computer or telephone equipment to the local loop. The connection between these devices and the public network is done by means of a user modem.

The local loop is controlled by the local loop operator. A cabinet called "dispatch cabinet" concentrates all lines of subscribers from users before accessing the telephone switch on a pair of copper.

In FIG. 2, a transmitter / receiver 6 connected to the telecommunications equipment of the operator (not shown) is connected via the local loop 2 to a modem 8 or DSL router (called HTU-R in the international specifications IUT- T or ETSI).

The receiver 6 comprises a module for detecting the presence of one or more carriers as defined by the ITU-T G.994.1 standard and a module for identifying the type of the detected carrier among the following standard types: A43, B43 , C43, A4.

If the detected carrier is of the A43 type, it is deduced that the modem connected to the user installation is either an ADSL modem of the DMT AoI type (for ADSL over

ISDN, that is to say ADSL on integrated services digital network) ISDN, or an ADSL modem type G.lite type AoP (for ADSL over POTS, that is to say ADSL on a local loop) or type AoI.

If the carrier is of the B43 type, it is deduced that the modem connected to the user installation is of the DMT AoP type.

If the carrier is of the C43 type, it is deduced that the modem connected to the user installation is either an ADSL modem of the DMT AoP type where the cable is shared with ISDN services, an G.Lite type ADSL modem of the AoP type where the cable is shared with ISDN services, or an SSDSL type modem.

If the carrier is of type A4, it is deduced that the modem connected to the user installation is of type G. SHDSL.

If the carrier does not belong to any of the standard types described above, it is inferred that there is no active HSTU-R modem on the line. When an HSTU-R modem is connected to the end of the subscriber line, receiver A measures the frequency and amplitude of each detected carrier, compares the measured amplitude for each detected carrier with a theoretical amplitude associated with that carrier. carrier and calculates the attenuation of each carrier in the copper pair 2 from the theoretical level.

FIG. 3 represents an experimental curve illustrating the evolution of attenuation in a given cable as a function of the frequency of the signals that flow through this cable. This curve makes it possible to determine the attenuation of the carriers detected in the copper pair. From this information, the terminal A extrapolates the attenuation in the copper pair at particular frequencies different from the normalized frequencies.

Recall that each type of cable deployed by a telecommunications operator on its local loop corresponds to a model of attenuation (dB) per kilometer of cable as a function of frequency. There is then a report, and therefore a single coefficient between the attenuation at any reference frequency and each of the attenuations at frequencies used by the HTU-R modems to transmit their carriers. Thus for French cables a ratio of 1.42 is observed between the attenuation at 300 kHz

(reference frequency) and that measured on the third carrier (107.83 kHz) of HTU-R type AoP.

For German cables, a ratio of 1.12 is observed between the attenuation at 300 kHz (reference frequency) and that measured on the third carrier (228.60 kHz) of HTU-R type AoI.

In Figure 4, ai, a ₂ and a ₃ respectively represent the attenuation of the carriers transmitted by a modem HTU-R respectively to the frequencies f _lr I ₂ and f ₃ normalized to a transmission cable of the type used in the local loop.

The extrapolation of the attenuation at a given frequency f _d is carried out by the terminal A according to the following steps: a) Acquisition of the signal in line, b) Frequency analysis of the signal measured by Fast Fourier Transform (TFR or FFT for Fast Fourier Transform) to obtain the spectrum of the measured signal. An example of a result of this analysis step is illustrated in FIG. 5 indicating the evolution of the amplitude of the signal as a function of frequency. c) Search for measured levels at the normalized carrier frequencies of HTU-R modems, d) Comparison of these levels with a maximum threshold and a minimum threshold, e) Verification of the presence of at least one of these carriers between these two thresholds.

If the level of at least one of the carriers is between the two thresholds, then it is deduced that a modem type HTU-R is connected to the end of the line. The extrapolation of the attenuation to detected carriers at the desired frequency f _d is to multiply the attenuation of the carrier detected by the associated coefficient. If for example in France the third carrier (107.83 kHz) of a type AoP HTU-R is measured with a loss of 1OdB, the attenuation of the line at 300 kHz is:

10 * 1.42 = 14.2 dB.

In Germany, if the third carrier (228.60 kHz) of a type AoI HTU-R is measured with a loss of 1OdB, the attenuation of the line at 300 kHz is then:

10 * 1.12 = 11.2 dB.

The invention makes it possible, for a type of cable used in the local loop of an operator, to deduce attenuation at arbitrary frequencies, from attenuation models at standard frequencies for this type of cable.

Claims

1. A method for evaluating the attenuation, at a given frequency, of the signals transmitted on a copper pair connecting a user installation to a local loop, characterized in that it comprises the following steps: a) detecting the presence on said pair of copper of at least one normalized carrier, b) measuring the amplitude of the detected carrier, c) comparing the measured amplitude with a predefined theoretical amplitude for said normalized carrier, d) calculating the attenuation of the normalized carrier detected on the copper pair from step c); e) deducing from step d) the attenuation, at said particular frequency, of the signals transmitted via said pair of copper.

2. Method according to claim 1, characterized in that the connection between the user facility is connected to the local loop by a broadband channel DSL type.

3. Method according to claim 1, characterized in that step f) is performed from a predefined attenuation model representative of the local loop of a given operator.

4. Method according to claim 1, characterized in that the standardized carrier belongs to one of the following standard types defined by TU-T G.994.1: A43, B43, C43 or A4.

5. Device for evaluating the attenuation of the transmitted signals, at a predefined frequency, on a copper pair (2) connecting a user installation

(8) to a local loop (4), characterized in that it comprises: means for detecting the presence on said pair of copper (2) of at least one normalized carrier, means for measuring the amplitude of the detected carrier, means for comparing the measured magnitude to a predefined theoretical magnitude associated with said normalized carrier, means for calculating attenuation of the normalized carrier detected on the copper pair (2) from step d) means for deriving the attenuation, at said particular frequency, of the signals transmitted via said pair of copper from the attenuation of the detected carrier.

6. Device according to claim 5, characterized in that it further comprises a measuring equipment connected to one end of the copper pair and a DSL modem connected to the user installation.