WO2002028111A2

WO2002028111A2 - Improved technique for remote power feeding of telephone subscribers

Info

Publication number: WO2002028111A2
Application number: PCT/IL2001/000891
Authority: WO
Inventors: Barzilay Mizrahi; Moti Heller
Original assignee: Inovia Telecoms Ltd.
Priority date: 2000-09-28
Filing date: 2001-09-24
Publication date: 2002-04-04
Also published as: IL138759A; WO2002028111A3; IL138759A0; AU2001294155A1

Abstract

A technology for improved power distribution between subscriber lines fed from an RU unit receiving power from an EU unit through a DSL line, the technology comprising: - defining a maximal value of a current Idsl (Idslmax) allowed to be input to the RU unit from the DSL line; - monitoring the input current Idsl of the RU unit and producing a control signal when said input current exceeds the value Idslmax; - dynamically distributing output current of the RU unit between the subscriber lines according to their respective consumption as long as the input current is in the range 0≤ Idsl ≤ Idslmax, while limiting the output current consumption by said subscriber lines upon receiving the control signal that said Idslmax is exceeded.

Description

Improved technique for remote power feeding of telephone subscribers

Field of the invention

The invention relates to access systems of telecommunication networks, and particularly to a system and a method for effective use of feed power supplied by a local exchange to multiple subscribers thereof.

Background of the invention

Systems for providing power feed to subscribers of so-called wire-line access networks can be divided into two main categories: 1) systems where the subscribers have autonomous power supply independent from any remote power feed, and 2) systems where the subscribers are fed by power conducted to them by copper wires (closed loop or U-loop) from a remote central station (public switch, or local exchange) via intermediate units such as EU (exchange unit) and RU (remote unit), and wherein the same loop is used for transmitting voice or data. The wire-line (i.e., not wireless) access networks usually comprise one or more DSL (Digital Subscriber Line) for transmitting data and power to PSTN (Public Service Telephone Network). In DSL operation, a pair of copper wires provides both the power to operate remote functional blocks, and enables transferring digital data through the copper wires. There is also known a hybrid system, where the autonomous power feed is activated when the remote power feed fails by any reason.

Those skilled in the art are familiar with access networks where a subscriber of a particular Central Office is connected to it via a physical wire-line chain of signal and power distribution units (such as EU and RU), which by stages perform operations of multiplexing/demultiplexing of the transmitted/received signals.

Fig. 1 depicts a typical DSL installation. It comprises a public switch

(CO) 10 which is connected to an exchange unit (EU) 12 by means of a Tl/El interface. From the EU 12, a number of DSL lines are connected to respective RU units. A remote unit RU (16) receives the DSL signal and demultiplexes it to transmit its data components onto a number of respective U-loop subscriber lines 18. Each of the U-loops is equipped with a Network Terminator (NT) 20 providing physical and electrical termination of the local loop between the carrier network and the user premise. Typically, NT may support up to eight user's terminal devices 21 (telephones, computers and fax machines). It goes without saying that the communication is routinely kept in the opposite direction as well. A particular example of the system parameters is presented below, the parameters being calculated for a cable having the specific resistance of 266 Ohm/Km.

In a particular PCM system, one EU block produces, at its output stage, a plurality of DSL lines (14) wherein each DSL line is specified for a distance not exceeding 3 km and a maximal resistance (say, 800 Ohm). The output power from EU to each DSL is limited due to safety reasons. The output current from EU to each DSL is standardized by a Standard Recommendation ITU-T K.50 and shall never exceed 60MA. (Other standards may state different values for this current.) The EU output voltage for the illustrated architecture is agreed between a provider of the communication service and a particular vendor. In this case it is limited to 320V dc. Each RU unit is designed to support up to five ISDN NT blocks via respective U-lines. As typically accepted, each of the five U-lines is designed equally to the others; say, it is specified for a maximum distance 4.5 Km which is equivalent to a U-line resistance of 1200 Ohm. The output power from the RU to each U- line is obtained by multiplying a predetermined RU output voltage 100V and current 20MA at the steady state. The current 20 niA per each U-line is a result of dividing the RU total output current by 5, wherein the total output current is calculated using the power provided on the RU output and the predetermined RU output voltage required by local rules. The standardized or constant values are marked in the figure by asterisks.

The above-specified distances for the DSL line and for the U-line are calculated from available power budget in the system, and based on the so-called "worst case" for a particular number of subscribers. The worst case is understood as a case when all the subscribers are actively using their respective U-loops.

In practice, some subscribers of a particular RU can be located closer to it than stated by the maximal recommended distance, so the power consumption of such subscriber lines is reduced due to reduction of the U-loop resistance. However, other U-lines supported by the same RU cannot benefit from that, since they continue receiving their predetermined allowed output power portion f om the RU, which is equal for each of the neighboring loops. Actually, the RU possesses an extra power, which is not utilized by its subscribers. In such a configuration, when one of the U-lines is slightly longer than the designed length and thus consumes more current, the extra current cannot be provided from other U-lines even if at the particular case they are not consuming the maximal current they are designed for. To the best of the Applicant's knowledge, no means are described in the prior art of how standardized equipment of DSL systems could utilize power budget of the system more effectively. Object of the invention

It is the object of the present invention to provide a technique for effective utilizing power budget of a communication system including a

DSL line and a number of subscribers, and for subscriber lines' flexible arrangement.

Summary of the invention

The solution has come from recognizing the fact that the maximal theoretic length of a subscriber's copper U-line at which it is still capable of delivering data to/from the subscriber is never used in the above-specified systems due to the absence of a safe mechanism of power sharing. Indeed, would the U-lines be designed for the maximal theoretic length, there could often be a danger of over-consumption of the RU output power. Such a mechanism, if existed, would be capable of ensuring operation of any possible configuration of the system, including those comprising extremely long U-lines.

The above object can be achieved by providing a method of improved power distribution for remote feeding a number of subscriber lines from a local exchange via a chain comprising an EU unit, a DSL line and an RU unit, the method comprising:

- defining a maximal value of a current I_dsl allowed to be input to the RU unit from the DSL line, said maximal value being I_dsimax; - monitoring the input current I_dsι of the RU unit and producing a control signal whenever said input current exceeds the value I_dsιmax;

- dynamically distributing output current of the RU unit between the subscriber lines according to their respective consumption as long as the input current is in the range 0< I_dsl < I _sιmax, while limiting the output current consumption by said subscriber lines upon receiving the control signal that said I _sιmax is exceeded.

It should be understood that "DSL" is a generic name for a family of digital lines (also called xDSL) being provided by local exchanges and local telephone companies to their subscribers. These include, for example, ADSL, SDSL, VDSL, etc.

Similarly, it is to be mentioned that the terms EU and RU are used for the sake of compactness only and should be understood in the following general meaning: EU (exchange unit) - an electronic system for signal and power distribution, usually allocated at the side of a local exchange; at its input stage EU interacts with the standard interface of the local exchange (such as El, Tl), and at its output stage produces one or more xDSL lines;

RU (remote unit) - an electronic system for signal and power distribution installed between the EU and a number of subscribers; at its input stage RU is connected to an xDSL line, and at its output stage - to one or more subscribers' lines.

The method allows safe power balancing in any RU-subscribers system, including the known typical systems not including extra long subscriber lines. In such systems, the method allows one U-line to

"borrow" extra current from a neighboring U-line, when any line started consuming more power than previously designed (say, the installed

U-line in practice slightly exceeded the distance which was considered maximal). In practice, the method can be accomplished if the step of monitoring is performed by providing an input current sensor at the RU input stage capable of producing said control signal when the input current exceeds the value I_dsιmax, and the step of dynamic current distribution being ensured by providing a limiting distribution circuit at the RU output stage for distributing power output from the RU unit between said subscriber lines, and by arranging said input current sensor to control said limiting distribution circuit so as to ensure free distribution of the power output from the RU unit between said subscriber lines per their current consumption, when the input current is in the range 0< I_dsι < I _sιmax, and to automatically limit the energy consumption in said subscriber lines when said I_dsιmax is exceeded. The method is even more advantageous for non-standard systems, where at least one subscriber's line has the maximally allowed resistance still allowing delivering data to the subscriber (Rumax), and therefore consumes in its active condition a U-line current which is higher than other, shorter subscribers' lines may consume. This lumax is calculated as a current required to be fed to a subscriber line having the maximal theoretically allowed line resistance.

The way and examples of calculation of the maximally allowed values of resistance Rumax, distance and current lumax can be found in the detailed description. The free distribution of the output power of the RU unit means that in the defined interval of values of the I_dsι the subscribers will be provided with power per their respective needs and according to their respective limits from the common source being the RU output stage equipped with the current distributing circuit. To ensure the free current distribution in the system having at least one extra long subscriber's line capable of consuming the maximally allowed current lumax, the method preferably comprises a step of providing any one of the subscriber lines with a current limiting circuit adjusted to the lumax. In practice, the shorter lines never consume such a current, though the equal current limiting circuits facilitate the balancing in the system.

Since, according to the method, input current of the RU is clipped to the maximal allowed value while output currents (and powers) of the RU are restricted to the "theoretical" maximal lu max, the method allows that at least one of the subscriber lines be arranged to supply this current to its subscriber(s) located at a "theoretical" maximal distance from the

RU unit, exceeding the typically used one.

The described method also allows taking advantage of differences in power consumption when different lengths of the DSL line are selected. By adjusting the DSL resistance when installing the line, a wider range of parameters of the subscriber lines can be obtained for selection.

According to another aspect of the invention, there is provided an electronic system for effective utilizing power budget of a DSL access network. Yet another aspect of the invention relates to a device (RU) incorporating the electronic system.

The electronic system, for improved power distribution between subscriber lines fed from an RU unit receiving power from an EU unit through a DSL line, comprises:

- an input current sensor at the RU input stage for monitoring the RU input current I_dsι and producing a control signal when said input current exceeds the value I_dsιmax;

- a limiting distribution circuit at the RU output stage for distributing power output from the RU unit between said subscriber lines, controllable by said input current sensor so as to ensure free distribution of the power output from the RU unit between said subscriber lines per their current consumption as long as the input current is in the range 0< I_dsι < I_dsιmax, and to automatically limit the energy consumption in said subscriber lines when said I_dsιmax is exceeded.

Therefore, when the subscriber lines are "allowed" to consume as much power as technically possible from the RU which still consumes the input current not exceeding I_dsιmax, there is automatically maintained a dynamic power distribution between the RU outputs (i.e., between the subscribers).

Preferably, the system according to the invention comprises at least one subscriber's line having a maximally allowed resistance (Rumax) still allowing delivering data to the subscriber, and capable of consuming, in its active condition, a U-line current lumax which is higher than other, shorter subscribers' lines may consume. (This lumax current can be calculated as a feeding current from a known source (the RU unit) to a subscriber line having the maximal theoretically allowed line resistance). Preferably, the system having at least one extra long subscriber's line capable of consuming the maximally allowed current lumax, comprises a current limiting circuit adjusted to said lumax and installed on each of the subscriber lines.

Further aspects and details of the invention will be disclosed as the description proceeds.

Brief description of the drawings

The invention will further be described with the aid of the following non-limiting drawings in which: Fig. 1 (prior art) is a schematic block-diagram of a typical DSL installation in the access network, comprising CO, EU unit, RU units,

DSL lines and subscribers' U-lines.

Fig. 2 is a schematic block-diagram of a DSL access configuration which, after providing a particular electronic circuit to the RU power supply, enables flexible power distribution between the subscribers' lines.

Fig. 3 is a schematic diagram of the electronic circuit capable of distributing current/power between subscriber lines of RU unit.

Fig. 4 is a graphical representation of options for selecting ratios between the DSL line resistance and the U-line(s) resistance which are open for implementation in a system for remote feeding of subscribers according to the proposed invention.

Detailed description of the preferred embodiments

Coming back to Fig. 1 (prior art) one may notice that Remote Units RU-1 and RU-n are located at different distances from the EU unit 12 i.e., the respective DSL lines have different lengths. It should be noted, that their lengths are within the allowed range 3km (or 800Ohm) limited as the recommended DSL distance for this particular system. The analogous situation takes place with respect to the U-lines connected to the RU units. As one may recall, each of the RU units 16 can be connected to five subscriber lines 18. Output voltages of RU are agreed and constant, and the subscriber currents of RU are all limited to a particular value calculated for the worst case. Fig. 2 illustrates a modified access network, where RU is provided with an electronic device, according to the invention, which will be described with reference to Fig. 3. In the illustrated access network, the RU units 26 and 28 are differently distanced from the EU unit 12. RU unit 26 is connected to five subscriber U-lines, wherein one of them (30) which carries Network Terminator NT-5 is essentially longer than the remaining lines not exceeding the typically recommended U-line length. RU unit 28 is connected to three subscriber lines, which are all much longer than the recommended length (if compared to Fig.l).

An example of calculating power budget of RU 26 in the illustrated configuration is presented below, compared to the typical configuration.

The system parameters (standard or agreed safety regulatory values) are marked *.

The "Maximum" column of the system parameters is used for the calculation:

Input power to the Remote Unit:

Pi(RU) = Vdsl * Idsl - Idsl² * Rdsl = 15AWatt (where Rdsl is selected to be 800 Ohm.) Output power from the RU to 5 U lines [Po_t(U)]:

Po_t{U) = Pi(RU)*η-P(RU) = 10.9 Watt

Total output current from the RU, say to 5 U-lines [Iu_t] : Iu_t = Po JIVu = 112mA

If all the U-line distances are designed equal as in a typically recommended system, then the maximal current in one subscriber line [lu] for the worst case :

Iu=Iuj/5=22.5mA

And maximum possible resistance of the U loop would be stated as:

Ru = (Vu * 7« - P(NT))/Iιι² = 1200Ω Which means that the maximal distance would be 4,5 Km.

If, according to the invention, at least one of the U-lines is desired to be maximally long so as to allow serving a subscriber (NT-5) located farther than 4,5 Km , it is proposed that the resistance of this U-line (Ru-max) be considered equal to 1500 Ohm (see N.B. below) i.e., the theoretical maximal resistance corresponding to 5,63 Km, so that

Ru = (Vu *Iu- P(NT)) I lu² = 1500Ω

and therefore, for the same Vu and P(NT) the maximal lu current of the U-line 1 [Iu_max l]will be: Iu nax 1 = 32 mA.

To serve other four U-lines which can be shorter than the typically recommended, their maximal currents can be selected as follows:

Iujnax 1, 2, 3, 4 = (Iu_t~Iu_maxl)/4= 20 mA, Ru_l, 2,3,4 calculation gives 900 Ohm for each of the lines, thus lengths of the respective U-lines can be up to 3,4 Km.

N.B. The Rujmax can be calculated as follows:

Knowing that

Ru=(Vu*Iu — P(NT)) /lu , let's differentiate this equation and equal it to zero to obtain its maximum:

-Vu/Iu² + 2P(NT)/f =0 or lu =2P(NT)/Vu, which is the current if the Ru is maximal. Substituting lu in the initial equation, we receive:

Ru nax = Vu /4p(NT).

For the above example, it will be:

Rujnax = 98²/ 4*1.6 = 1500.625 (Ohm)

To allow safe power distribution in such a configuration, the RU unit is provided with an electronic system, one embodiment of which is illustrated in Fig. 3 and will be described below.

The illustrated configuration of the network is advantageous in that it is both adapted and adjustable to real requirements of subscribers and to real limitations of the network developers and operators. Fig. 3 schematically shows input and output interior circuits of the

RU unit, which form together an electronic system for power distribution.

Circuit 32 constitutes the input current sensor; it is coupled to the incoming DSL line and connected to a rectifying bridge 34. The function of the circuit 32 is to monitor whether the incoming current I_dsι is within its predetermined maximal range. The I _sιmax for EU units supporting

DSL lines is stated to be 60 mA by one of the standards.

Vref-1 is adjusted for the stated I_dsιmax, and the sensor is ready for monitoring the DSL line. The input current I_dsj is measured on Rs (marked 36) and applied to a first operational amplifier 38. The output of the first amplifier is fed to one input of a second operational amplifier 40 which compares it with the precise (i.e., preliminarily adjusted) reference voltage Vref-1. If the incoming current does not exceed I_dsι max, an opto-isolator 42 is preserved in its OFF condition. Whenever the value of I_dsι max is reached and starts increasing, the opto-isolator 42 turns ON, i.e., its light diode starts illuminating its light effect transistor.

The incoming I_dsι current, being converted by a High Voltage DC/DC Converter 43 of the RU unit, at its output stage (marked by "+" and "-" and generally by 44) produces the output voltage Vu and the total output current Iu_t. The output current Iu_t is distributed by a limiting current distribution circuit (generally marked 46) and, being split into "n" U-line currents, creates output voltages on "n" outputs of the RU unit intended to feed U-lines from Ul to Un. In the drawing, the RU outputs are marked 48, 50 and 52. The limiting current distribution circuit 46 at its input is coupled to the output stage of the RU unit, and its output - to "n" individual current limiting subscriber circuits 54 connected in parallel to the common portion and serving the respective outputs 48, 50 and 52. Current limit values of the circuits 54 is set by their input voltage dividers, and are equal in this embodiment. A load of the first subscriber's line is schematically shown by a dashed line and marked 56. The limiting current distribution circuit 46 is switchable by the light effect transistor of the opto-isolator 42. When the input current I_dsι is lower than the maximal value, the opto-isolator 42 is closed and voltage Vref-com is high, since is not affected by the transistor of the opto-isolator and depends only on the voltage limitation Vref-2 provided by the precise Zener diode 53. So, when the transistor of the opto-isolator 42 does not conduct and the Vref-2 (solely) causes a high Vref-com, the subscriber lines consume currents per their needs and according to their own current limits which in this particular example are selected higher than the "worst case" current for the subscriber U-line (for example, 34 mA instead of 22,5 mA recommended). Consequently, also high is the output of a third operational amplifier 58 providing more drive to a FET Ql (marked 60) and as a result, allowing higher output current to the Ul line which is able to compensate for additional distance. Simultaneously, other outputs are controlled by the same Vref-com in the analogous manner, and may consume higher or lower currents from Iu_t, according to requirements of the respective U-lines with their subscriber terminals and Vref-com. The current balancing is dynamic, i.e. the current regulation circuit 44 re-distributes power received from the DSL line according to working conditions of the active U-lines. It is understood, that portion of the RU input power is always consumed to internal needs of the RU unit.

If the I_dsι starts exceeding I_dsι max (say, one or more of the subscribers changed load in their premises and the consumed power grew, or there is a fault in the line), the transistor 42 of the opto-isolator starts conducting, so the Vref-com will be reduced, thereby gradually limiting Iu_t (the budget from which the subscribers' currents are taken) to the pre-designed maximum. The decreased reference voltage Vref-com is applied to the third operational amplifier 58 which alters the bias to the output of FET 60 and at a particular point lowers the current flowing via this specific U-line. It is understood that the greatest lu current will be reduced first. This may temporarily disturb operation of U-lines, which were extended over the recommended distance, though is likely to happen only in fault situations. When essential changes are introduced in the access network (e.g., appearance of additional U-lines or adding quite a lot of equipment to be fed by one of the U-lines - say, organizing a small office LAN), an operator should take care of recalculating the system.

Fig. 4 shows a graph built by the Inventors to reflect mutual dependence between resistance of the DSL line and resistance of U-lines in a system comprising EU, DSL and RU supporting five similar U-lines (a solid line). The point on the graph having coordinates Rdsl =800 Ohm and Ru =1200 Ohm is the typical point according to which the "worst case" values are usually developed for such systems. Using a developed program product, the Inventors calculated and demonstrated how, at particular values of Rdsl and other constant or agreed parameters, one of the U-lines can be elongated to approach the theoretically maximal resistance (a dotted line).

According to an additional aspect of the invention, there is provided a computer program product for use with the described RU unit, the product comprising a computer usable medium having a computer readable program for calculating parameters (such as voltages, currents and powers) of a system comprising the EU block, the RU block, a DSL line connecting the EU block with the RU block and a number of U-lines respectively connecting the RU block to subscribers. The program is capable of calculating said parameters for various combinations of resistance of the DSL line and the subscribers' U-lines.

It should be appreciated, that other embodiments of the electronic power distribution circuit can be proposed, which are to be considered part of the invention if they fulfil the purpose of the invention. Also, the DSL line in the present description and claims should be understood as any physical line capable of transmitting power and a number of voice/data channels to remote subscribers. As well, the EU and RU are just terms which should be understood as indicating functional blocks for power and signal distribution in telecommunication networks.

Claims

Claims:

1. A method for improved power distribution between subscriber lines fed from an RU unit receiving power from an EU unit through a DSL line, the method comprising: - defining a maximal value of a current I_dsι allowed to be input to the RU unit from the DSL line, said maximal value being I_dsιmax;

- monitoring the input current I_dsι of the RU unit and producing a control signal when said input current exceeds the value I_dsιmax;

- dynamically distributing output current of the RU unit between the subscriber lines according to their respective consumption as long as the input current is in the range 0< I_dsι < I_dsιmax, while limiting the output current consumption by said subscriber lines upon receiving the control signal that said I_dsιmax is exceeded.

2. The method according to Claim 1, wherein the step of monitoring is performed by providing an input current sensor at the RU input stage capable of producing said control signal when the input current exceeds the value I_dsιmax, and the step of dynamic current distribution is ensured by providing a limiting distribution circuit at the RU output stage for distributing power output from the RU unit between said subscriber lines, and by arranging said input current sensor to control said limiting distribution circuit so as to ensure free distribution of the power output from the RU unit between said subscriber lines per their current consumption, when the input current is in the range 0< I_dsι < I_dsιmax, and to automatically limit the energy consumption in said subscriber lines when said I_dsιmax is exceeded.

3. The method according to Claim 1 or 2, further comprising a step of selecting, for a specific resistance of the DSL line, at least one subscriber's line having a maximally allowed resistance (Rumax) still allowing delivering data to its subscriber so that said subscriber's line is capable of consuming a current lumax.

4. The method according to Claim 3, further comprising a step of limiting current in all of the subscriber lines to said lumax.

5. An electronic system for improved power distribution between subscriber lines fed from an RU unit receiving power from an EU unit through a DSL line, said system comprising:

6. The electronic system according to Claim 5, for a configuration including at least one subscriber's line having a maximally allowed resistance Rumax and capable of consuming a maximally allowed current lumax, the electronic system comprising current limiting circuits switched in the respective subscriber lines, any one of the current limiting circuits being adjusted to said lumax.

7. An RU unit equipped with the electronic system according to Claim 5 or 6.

8. A computer program product for use with the RU unit according to Claim 7, the product comprising a computer usable medium having a computer readable program for calculating parameters of a system comprising the EU block, the RU block, a DSL line connecting the EU block with the RU block and a number of subscriber lines respectively connecting the RU block to subscribers; said program being capable of calculating said parameters for various resistance combinations of the DSL line and the subscriber lines.