Device, method and system for estimating the termination to a wired transmission-line based on determination of characteristic impedance Number:7,521,943 from the United States Patent and Trademark Office (PTO) owispatent

Title: Device, method and system for estimating the termination to a wired transmission-line based on determination of characteristic impedance

Abstract: A system and method for measuring a characteristic impedance of a transmission-line comprises transmitting energy to the line, and shortly after measuring the voltage/current involved and thus measuring the equivalent impedance. The measured characteristic impedance may then be used in order to determine the termination value required to minimize reflections. In another embodiment, the proper termination is set or measured by adjusting the termination value to achieve maximum power dissipation in the terminating device. The equivalent characteristic impedance measurement may be used to count the number of metallic conductors connected to a single connection point. This abstract is not intended to limit or construe the scope of the claims.

Patent Number: 7,521,943 Issued on 04/21/2009 to Binder,   et al.

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Inventors:	Binder; Yehuda (Hod Hasharon, IL), Hazani; Ami (Ra'anana, IL)
Assignee:	Serconet, Ltd. (Ra'anana, IL)
Appl. No.:	11/091,371
Filed:	March 29, 2005

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Foreign Application Priority Data

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Jan 23, 2005 [IL]			166445

Current U.S. Class:	324/691 ; 324/71.1
Current International Class:	G01R 27/08 (20060101); G01R 27/00 (20060101)
Field of Search:	324/691,713,66,71.1

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References Cited [Referenced By]

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U.S. Patent Documents

5010399	April 1991	Goodman et al.
5193108	March 1993	Stocklin
5621455	April 1997	Rogers et al.
5633801	May 1997	Bottman
5734658	March 1998	Rall et al.
5841360	November 1998	Binder
5896443	April 1999	Dichter
6069899	May 2000	Foley
6108331	August 2000	Thompson
6216160	April 2001	Dichter
6243571	June 2001	Bullock et al.
6351533	February 2002	Parrott
6396391	May 2002	Binder
6480510	November 2002	Binder
6549616	April 2003	Binder
6560319	May 2003	Binder
6625005	September 2003	Otsuka et al.
6690677	February 2004	Binder
6842459	January 2005	Binder
6927340	August 2005	Binder
6937056	August 2005	Binder
6956826	October 2005	Binder
7106721	September 2006	Binder
7317793	January 2008	Binder
2002/0019966	February 2002	Yagil et al.
2002/0039388	April 2002	Smart et al.
2002/0060617	May 2002	Walbeck et al.
2002/0146207	October 2002	Chu
2002/0166124	November 2002	Gurantz et al.
2002/0194383	December 2002	Cohen et al.
2003/0062990	April 2003	Schaeffer, Jr. et al.
2003/0099228	May 2003	Alcock
2003/0112965	June 2003	McNamara et al.
2003/0139151	July 2003	Lifshitz et al.
2004/0125819	July 2004	Binder
2005/0010954	January 2005	Binder
2005/0025162	February 2005	Binder
2005/0047431	March 2005	Binder
2005/0129069	June 2005	Binder
2005/0180561	August 2005	Hazani et al.
2005/0249245	November 2005	Hazani et al.

Foreign Patent Documents

	0 768 537		Apr., 1997		EP
	WO 02/25920		Mar., 2002		WO
	WO 02/065229		Aug., 2002		WO
	WO 2004/001034		Dec., 2003		WO

Other References

Fowler, Bill, "Transmission Line Characteristics", National Semiconductor Application Note 108, National Semiconductor Corporation, Jul. 1986, pp. 1-8. cited by other . True, Kenneth M., "Reflections: Computations and Waveforms", National Semiconductor Application Note 807, National Semiconductor Corporation, Mar. 1992, pp. 1-25. cited by other . True, Kenneth M., "Long Transmission Lines and Data Signal Quality", National Semiconductor Application Note 808, National Semiconductor Corporation, Mar. 1992, pp. 1-23. cited by other . True, Kenneth M., "Data Transmission Lines and Their Characteristics", National Semiconductor Application Note 806, National Semiconductor Corporation, Apr. 1992, pp. 1-7. cited by other . Vo, Joe, "A comparison of Differential Termination Techniques", National Semiconductor Application Note 903, National Semiconductor Corporation, Aug. 1993, pp. 1-10. cited by other . Strassberg, Dan; "Home Automation Buses: Protocols Really Hit Home"; EDN Design Feature, Apr. 13, 1995 (9 pages). cited by other . Hachman, Mark; "Compaq to Ride The CEBus"; EBN Jan. 22, 1996 (1 page). cited by other . Hoffman, J.; "Cable, Television, and the Consumer Electronic Bus"; Panasonic Technologies. Inc., pp. 165-173, no date. cited by other . IS-60.04; Node Communications Protocol Part 6: Application Layer Specification; Revision Apr. 18, 1996, (129 pages). cited by other . Markwalter, Brain et al; "CEBus Router Testing"; IEEE Transactions on Consumer Electronics Nov. 1991, vol. 37 No. 4 (8 pages). cited by other . Grayson Evans, The CEBUs Standard User's Guide, 1st edition, May 1996, 317 pages. cited by other.

Primary Examiner: Dole; Timothy J
Attorney, Agent or Firm: Browdy and Neimark, P.L.L.C.

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Claims

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The invention claimed is:

1. A method for estimating the number of wire pairs connected to a single connection point, where each wire pair has a similar nominal characteristic impedance Z0, the method comprising: connecting a characteristic impedance measuring device to the single connection point; measuring, at the connection point, the lumped impedance Z presented by the wire pairs adjacent the connection point; calculating Z0/Z to provide an estimate of the number of wire pairs connected to the single connection point; and providing an output indicating the estimate of the number of wire pairs connected to the single connection point.

2. The method according to claim 1, further comprising storing a representation of the estimate of the number of wire pairs.

3. The method according to claim 2, further comprising providing a visual indication of the estimate of the number of wire pairs.

4. The method according to claim 1, wherein said step of providing an output comprises providing a visual indication of the estimate of the number of wire pairs.

5. The method according to claim 1, wherein the wire pairs are at least partially hidden in the wall of a building, the connection point is an outlet having a front faceplate, and connecting to the connection point comprises connecting to a connector on the front faceplate of the outlet.

6. The method according to claim 5, wherein the wire pairs form part of a telephone, AC power, or CATV wiring infrastructure, and the outlet is a telephone, AC power, or CATV outlet, respectively.

7. The method according to claim 6, wherein the infrastructure carries a signal in a first frequency band, and measuring the lumped impedance comprises transmitting energy to the connection point in a second frequency band distinct from the first frequency band.

8. The method according to claim 1, further comprising: identifying a wiring end-point having a single connection wherein the connection point lumped impedance is Z0, and connecting a termination to the connection point of the identified wiring end-point.

9. The method according to claim 1, wherein the wire pairs are at least partially hidden in the wall of a building, the connection point is an outlet, and connecting a characteristic impedance measuring device to the connection point comprises integrating the measuring device into the outlet.

10. The method according to claim 1, wherein a modem for communication is connected to the connection point, and said method further comprises a preliminary operation of disconnecting the modem from the connection point, and a subsequent operation of re-connecting the modem to the connection point.

11. The method according to claim 1, wherein measuring and calculating are initiated periodically, or upon application of an external signal.

12. The method according to claim 1, wherein said step of measuring is carried out in a manner to exclude the influence of reflections along each wire pair.

13. The method according to claim 1, wherein said step of measuring is carried out to measure only the lumped impedance Z presented by the wire pairs.

14. A device for estimating the number of wire pairs connected to a single connection point, each wire pair has a similar nominal characteristic impedance Z0 and the wire pairs are all connected to the single connection point, said device comprising: a port for connecting to the connection point, a lumped impedance measuring unit coupled to said port for instantaneously measuring the connection point lumped impedance Z, a Z0/Z calculator coupled to the lump impedance measuring unit for estimating the connected wire pairs count to be Z0/Z; and an output for indicating the estimate of the number of wire pairs connected to the single connection point.

15. The device according to claim 14, further comprising a memory coupled to said lump impedance measuring unit for storing a representation of calculated number of wire-pairs.

16. The device according to claim 15, wherein said comprising means for providing an output provide a visual indication of the estimate of the number of wire pairs.

17. The device according to claim 14, further comprising a visual indicator for displaying the calculated number of wire-pairs.

18. The device according to claim 14, for use when the wire pairs are at least partially hidden in a wall of a building, the connection point is an outlet having a front faceplate, wherein said port comprises a connector that mates to a complementary connector on the front faceplate of the outlet.

19. The device according to claim 18, wherein the wire pairs form part of a telephone, AC power, or CATV wiring infrastructure, the outlet is a telephone, AC power, or CATV outlet, respectively, and said connector is a telephone, AC power, or CATV plug, respectively.

20. The device according to claim 19, wherein the infrastructure carries a signal in a first frequency band, and said lump impedance measuring unit comprises: an energy transmitter coupled to said connector for transmitting energy to the connection-point said energy being carried in a second frequency band distinct from the first frequency band.

21. The device according to claim 14, further comprising: means for identifying a wiring end-point having a single connection wherein the connection point lumped impedance is Z0, and means for connecting a termination to the connection-point of an identified wiring end-point.

22. The device according to claim 14, for use when the wire pairs are at least partially hidden in the wall of a building, wherein the connection point is an outlet, and said device is at least in part integrated into the outlet.

23. The device according to claim 14 for use with a modem for communication over the wire pairs, wherein the device further comprises a selective connection unit for disconnecting the modem from the connection point and for re-connecting the modem to the connection point.

24. The device according to claim 14, further comprising a selector for operating said device either periodically, or upon application of an external signal, or upon a manual action, or upon powering up of the device.

25. The device according to claim 14, wherein said measuring unit is operative to exclude the influence of reflections along each wire pair.

26. The device according to claim 14, wherein said measuring unit is operative to measure only the lumped impedance Z presented by the wire pairs.

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Description

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FIELD OF THE INVENTION

The present invention relates to the field of measuring transmission-line parameters, and specifically the characteristic impedance of a transmission line.

BACKGROUND OF THE INVENTION

Wired communication network topologies may generally be segmented into two types: Point-to-point and multi-point (also known as `point-to-multipoint`, `bus` and `shared medium`) networks. In point-to-point topology, the network employs one or more communication links, each link is based on a cable or wires as the communication medium and connects exactly two nodes, wherein each node is connected to an end of the cable. In multipoint configuration, multiple nodes are connected in parallel to the same wired medium is various points along the cable. Non limiting examples of point-to-point based communication networks are Local Area Network (LAN) Ethernet IEEE802.3 10BaseT, 100BaseTX, EIA/TIA-422 (a.k.a. RS-422), ISDN (U-Interface), EIA/TIA-449, IEEE1284, IEEE1394 and USB, and Wide Area Networks (WAN) such as HDSL (High speed Digital Subscriber Line), ADSL (Asymmetric Digital Subscriber Line) and other xDSL technologies (e.g. SHDSL, SDSL, VDSL, IDSL). Non-limiting examples of LANs employing multipoint topology are Ethernet IEEE802.3 10Base2, 10Base5, CAN, LON, and EIA/TIA-485 (a.k.a. RS-485). Other multipoint in-home networks include telephone line based communication such as HomePNA.TM. (Home Phoneline Networking Alliance), described in www.homepna.org, and powerline based communication such as HomePlug.TM., described in www.homeplug.org.

A non-limiting example of a unidirectional point-to-point communication link is shown as network 5 in FIG. 1. The network comprises a communication link based on two conductors 11a and 11b cable. A transmitter 14a is connected to one end of the cable at points 7a and 7b. Respective points 6a and 6b at the other end of the cable are connected to a receiver 13a and termination 12a. The signal is coupled to the cable by the transmitter 14a. The signal energy is propagated over the cable and absorbed by the termination 12a, and received by the receiver 13a.

The term `transmitter` herein includes any device which is capable of outputting energy or driving (or exciting) a signal, including an electrical signal, in a transmission-line. Such devices include line-drivers, modems and transceivers, as well as any other device having excitation capability. Such a signal may either be voltage based, current based or a combination of both. Similarly, the term `receiver` herein includes any device which is able to receive energy/signal (or any function thereof) from a coupled transmission line and convert it to an electrical form, including line receivers, modems and transceivers. Receivers are assumed herein not to include any termination functionality (such as very high input impedance).

A transmission-line is defined as a medium used to carry a signal from a point A to a point B. The terms `line`, `transmission line`, `cable`, `wiring`, `wire pair` as used herein should be interpreted to include any type of transmission-line, and specifically a metallic transmission line comprising two or more conductors used to carry electrical signals. Non-limiting examples are coaxial cable, PCB connections and twisted pair, the latter including both UTP (unshielded twisted-pair) and STP (shielded twisted-pair), as well as connections within Application Specific Integrated Circuits (ASICs). Characteristics of wired transmission-lines and their effect over digital data transmission are described for example in National Semiconductor Corporation Application Note 806 (April 1992) entitled: "Data Transmission Lines and their Characteristics", and in National Semiconductor Corporation Application Note 808 (March 1992) entitled: "Long Transmission Lines and Data Signal Quality". Characteristic impedance is a primary property of a metallic transmission line, and commonly relates to the instantaneous voltages and currents of waves traveling along the line.

The basic function of the termination 12a is to fully absorb the signal/energy propagating in the transmission line. Improper termination such as impedance mismatch will cause reflections (a.k.a ringing, overshoot, undershoot, distortion and resonance) back from the receiver-connected end to the transmitter-connected end. Such reflections will commonly degrade the communication characteristics of the communication link. Proper line termination becomes increasingly important as designs migrate towards higher data signal transfer rates over relatively longer lengths or transmission medium. For example, this may be applied to differential data transmission over two conductors such as twisted pair cable. In general, transmission-lines such as cables are treated as transmission-lines when the component wavelengths of the propagating signal, such as an electrical signal in a cable, is shorter than the physical length of the transmission-line. The importance of a proper line termination is discussed for example in National Semiconductor Corporation Application Note 108 (July 1986) entitled: "Transmission Line Characteristics". A proper line termination typically enables better ability to reliably recover a transmitted signal by using simpler means, as well as improving noise susceptibility.

Analysis of reflections can be found in the National Semiconductor Corporation Application Note 807, (March 1992) entitled: "Reflections: Computations and Waveforms", and the manner in which reflections impact on data transmission systems is described in the National Semiconductor Corporation Application Note 903 (August 1993) entitled: "A Comparison of Differential Termination Techniques".

Generally, in order to avoid reflection, the termination impedance should match the characteristic impedance of the transmission line in the frequency band of the discussed signal. If the cable parameters are known, and in particular its characteristic impedance (commonly designated as Z0), a good practice is to install a termination (a.k.a. terminator) 12a of the same value (Z0). In many cases, the cable parameters may be unknown. For example, the cable may exist in a wall and/or be of unknown type. Furthermore, cables may be manufactured with relatively large parameters tolerances, resulting in variations of characteristic impedance from batch to batch. Similarly, the characteristic impedance may change due to environmental conditions such as temperature, humidity and also over time. In any case wherein the cable parameters are not known, a measurement needs to be performed in order to establish the cable characteristic impedance, and accordingly terminating the line. Such measurement requires expertise, is labor extensive and time consuming.

There is thus a widely recognized need for, and it would be highly advantageous to have, a method and system for allowing easy and simple measuring of characteristic impedance, upon which a proper termination of a transmission line may be calculated, for example. Such system may be applied to transmission lines in general, and wired networks in particular, and specifically for a metallic transmission line having an unknown or changing characteristic impedance.

A multi-point based network (a.k.a. bus or multidrop network) is shown as network 10 in FIG. 1a. Two conductors 11a and 11b are used as the communication medium, wherein multiple nodes are connected thereto, each node connected at a distinct point along the line. The network is shown in a state wherein node 14a connected to the two conductors 11a and 11b of the line at respective connection points 18a and 18b is a transmitter, while all other nodes serve as receivers. Nodes 13a, 13b and 13c serve as receivers and are connected to the line at respective points (17a, 17b), (19a, 19b) and (9a, 9b) respectively. Similar to the above discussion, a termination (equal to the line characteristic impedance) is connected to each end, wherein terminations 12a and 12b are respectively connected to the transmission line ends (15a, 15b) and (16a, 16b).

Typically in wired communication, the wiring characteristic impedance is near pure resistance (non-complex impedance); hence each termination could be a simple resistor having a resistance equal to the characteristic impedance. Such resistors 23 are shown as terminations and are connected to the transmission line end points (such as 16a, 16b) of network 20 shown in FIG. 2.

While the metallic transmission line 5 shown in FIG. 1 is a non-tapped, single-path, homogenous and continuous wiring, a transmission line may sometimes involves a tap (a.k.a stub, bridge, and bridge-tap) or any other discontinuity. Such medium is shown in FIG. 2 as network 20. In addition to the two conductors 11a and 11b, the network employs an additional wiring part (a tap) comprising two conductors 21a and 21b, tapped in connection points 22a and 22b respectively. Similar to the above discussion, a termination is required in each line end, hence requiring resistor 23c connected across the tap end points 24a and 24b. Similarly, a wired network may employ multiple such taps. Hence for a line having arbitrary topology such as `star`, `tree` or any combination thereof, the taps may be without any node connection (such as shown in network 20), or may have nodes connected thereto. In addition, nodes may be connected to one or more of the line ends, in parallel to the termination.

In a multi-point environment, while termination is essential in all wiring ends in order to reduce reflections, it is equally important not to introduce termination at all points other than the cable ends. Any impedance connected will cause a mismatch and a signal propagated will introduce reflections at that point. As such, the nodes 13a, 13b and 13c should exhibit high impedance in their connection points to the transmission line.

In many cases, nodes (in particular receivers) comprise a built-in termination/resistor. If the node is connected in one of the line ends, the termination should be connected in parallel to the node. However, in a configuration wherein the node is not located in the line ends, the termination should be disconnected or disabled, in order to avoid generation of reflections. Such distinction between the connection locations complicates the network installation. Furthermore, in some cases the wiring topology is not easily known, such as in the case of in-wall existing wiring. Identifying the topology in order to distinguish between line ends and other points may be complex, labor intensive and expensive.

There is thus a widely recognized need for, and it would be highly advantageous to have, a method and system for allowing easy and simple termination of a transmission line in general, and wired networks in particular, and specifically for a metallic transmission line having multiple connection points, unknown to be either ends or in the middle of a wiring system.

Wired Home Networking.

Most existing offices and some of the newly built buildings facilitate a data network structure based on dedicated wiring. However, implementing such a network in existing buildings typically requires installation of new wiring infrastructure. Such installation of new wiring may be impractical, expensive and problematic. As a result, many technologies (referred to as "no new wires" technologies) have been proposed in order to facilitate a LAN in a building without adding new wiring. Some of these techniques use existing utility wiring installed primarily for other purposes such as telephone, electricity, cable television (CATV), and so forth. Such an approach offers the advantage of being able to install such systems and networks without the additional and often substantial cost of installing separate wiring within the building.

The technical aspect for allowing the wiring to carry both the service (such as telephony, electricity and CATV) and the data communication signal commonly involves using FDM technique (Frequency Division Multiplexing). In such configuration, the service signal and the data communication signals are carried across the respective utility wiring each using a distinct frequency spectrum band. The concept of FDM is known in the art, and provides means of splitting the bandwidth carried by a medium such as wiring. In the case of telephone wiring carrying both telephony and data communication signals, the frequency spectrum is split into a low-frequency band capable of carrying an analog telephony signal and a high-frequency band capable of carrying data communication or other signals.

A network in a house based on using powerline-based home network is also known in the art. The medium for networking is the in-house power lines, which is used for carrying both the mains power and the data communication signals. A PLC (Power Line Carrier) modem converts a data communication signal (such as Ethernet IEEE802.3) to a signal which can be carried over the power lines, without affecting and being affected by the power signal available over those wires. A consortium named HomePlug Powerline Alliance, Inc. of San Ramon, Calif. USA is active in standardizing powerline technologies. A powerline communication system is described in U.S. Pat. No. 6,243,571 to Bullock et al., which also provides a comprehensive list of prior art publications referring to powerline technology and application. An example of such PLC modem housed as a snap-on module is HomePlugl.0 based Ethemet-to-Powerline Bridge model DHP-100 from D-Link.RTM. Systems, Inc. of Irvine, Calif., USA. Outlets with built in PLC modems for use with combined data and power using powerlines are described in US Patent Application 2003/0062990 to Schaeffer et al entitled `Powerline bridge apparatus`. Such power outlets are available as part of PlugLAN.TM. by Asoka USA Corporation of San Carlos, Calif. USA.

Similarly, carrying data over existing in home CATV coaxial cabling is also known in the art, for example in US Patent application 2002/0166124 to Gurantz et al. An example of home networking over CATV coaxial cables using outlets is described in US Patent application 2002/0194383 to Cohen et al. Such outlets are available as part of HomeRAN.TM. system from TMT Ltd. of Jerusalem, Israel.

Telephony Definitions and Background

The term "telephony" herein denotes in general any kind of telephone service, including analog and digital service, such as Integrated Services Digital Network (ISDN).

Analog telephony, popularly known as "Plain Old Telephone Service" ("POTS") has been in existence for over 100 years, and is well designed and well engineered for the transmission and switching of voice signals in the 300-3400 Hz portion (or "voice band" or "telephone band") of the audio spectrum. The familiar POTS network supports real-time, low-latency, high-reliability, moderate-fidelity voice telephony, and is capable of establishing a session between two end-points, each using an analog telephone set.

The terms "telephone", "telephone set", and "telephone device" herein denote any apparatus, without limitation, which can connect to a Public Switch Telephone Network ("PSTN"), including apparatus for both analog and digital telephony, non-limiting examples of which are analog telephones, digital telephones, facsimile ("fax") machines, automatic telephone answering machines, voice (a.k.a. dial-up) modems, and data modems.

The terms "data unit", "computer" and "personal computer" ("PC") are used herein interchangeably to include workstations, Personal Digital Assistants (PDA) and other data terminal equipment (DTE) with interfaces for connection to a local area network, as well as any other functional unit of a data station that serves as a data source or a data sink (or both).

In-home telephone service usually employs two or four wires, to which telephone sets are connected via telephone outlets.

Home Networking Existing In-House Wiring.

Similarly to the powerlines and CATV cabling described above, it is often desirable to use existing telephone wiring simultaneously for both telephony and data networking. In this way, establishing a new local area network in a home or other building is simplified, because there is no need to install additional wiring. Using FDM technique to carry video over active residential telephone wiring is disclosed by U.S. Pat. No. 5,010,399 to Goodman et al. and U.S. Pat. No. 5,621,455 to Rogers et al.

Existing products for carrying data digitally over residential telephone wiring concurrently with active telephone service by using FDM commonly uses a technology known as HomePNA (Home Phoneline Networking Alliance) whose phonelines interface has been standardized as ITU-T (ITU Telecommunication Standardization Sector) recommendation G.989.1. The HomePNA technology is described in U.S. Pat. No. 6,069,899 to Foley, U.S. Pat. No. 5,896,443 to Dichter, U.S. Patent application 2002/0019966 to Yagil et al., U.S. Patent application 2003/0139151 to Lifshitz et al. and others. The available bandwidth over the wiring is split into a low-frequency band capable of carrying an analog telephony signal (POTS), and a high-frequency band is allocated for carrying data communication signals. In such FDM based configuration, telephony is not affected, while a data communication capability is provided over existing telephone wiring within a home.

Outlets

The term "outlet" herein denotes an electro-mechanical device, which facilitates easy, rapid connection and disconnection of external devices to and from wiring installed within a building. An outlet commonly has a fixed connection to the wiring, and permits the easy connection of external devices as desired, commonly by means of an integrated standard connector in a faceplate. The outlet is normally mechanically attached to, or mounted in, a wall or similar surface. Non-limiting examples of common outlets include: telephone outlets for connecting telephones and related devices; CATV outlets for connecting television sets, VCR's, and the like; outlets used as part of LAN wiring (a.k.a. structured wiring) and electrical outlets for connecting power to electrical appliances. The term "wall" herein denotes any interior or exterior surface of a building, including, but not limited to, ceilings and floors, in addition to vertical walls.

Functional Outlet Approach.

This approach involves substituting the existing service outlets with `network` active outlets. Outlets in general (to include LAN structured wiring, electrical power outlets, telephone outlets, and cable television outlets) have evolved as passive devices being part of the wiring system house infrastructure and solely serving the purpose of providing access to the in-wall wiring. However, there is a trend towards embedding active circuitry in the outlet in order to use them as part of the home/office network, and typically to provide a standard data communication interface. In most cases, the circuits added serve the purpose of adding data interface connectivity to the outlet, added to its basic passive connectivity function.

An outlet supporting both telephony and data interfaces for use with telephone wiring is disclosed in U.S. Pat. No. 6,549,616 entitled `Telephone outlet for implementing a local area network over telephone lines and a local area network using such outlets` to Binder. Such outlets are available as part of NetHome.TM. system from SercoNet Ltd. of Ra'ananna, Israel.

Another telephone outlet is described in U.S. Pat. No. 6,216,160 to Dichter, entitled `Automatically configurable computer network`. An example of home networking over CATV coaxial cables using outlets is described in WO 02/065229 published 22 Aug., 2002 entitled: `Cableran Networking over Coaxial Cables` to Cohen et al. Such outlets are available as part of HomeRAN.TM. system from TMT Ltd. of Jerusalem, Israel. Outlets for use in conjunction with wiring carrying telephony, data and entertainment signals are disclosed in US Patent Application US2003/0099228 to Alcock entitled `Local area and multimedia network using radio frequency and coaxial cable`. Outlets for use with combined data and power using powerlines are described in US Patent Application US2003/0062990 to Schaeffer et al. entitled `Powerline bridge apparatus`. Such power outlets are available as part of PlugLAN.TM. by Asoka USA Corporation of San Carlos, Calif. USA.

While the active outlets have been described above with regard to networks formed over wiring used for basic services (e.g. telephone, CATV and power), it will be appreciated that the invention can be equally applied to outlets used in networks using dedicated wiring. In such a case, the outlet circuitry is used to provide additional interfaces to an outlet, beyond the basic service of single data connectivity interface. For example, it may be used to provide multiple data interfaces wherein the wiring supports single such data connection. An example of such outlet is the Network Jack.TM. product family manufactured by 3Com.TM. of Santa-Clara, Calif., U.S.A. In addition, such outlets are described in U.S. Pat. No. 6,108,331 to Thompson entitled `Single Medium Wiring Scheme for Multiple Signal Distribution in Building and Access Port Therefor` as well as U.S. Patent Application US 2003/0112965 Published Jun. 19, 2003 to McNamara et al. entitled `Active Wall Outlet`.

While the active outlets have been described with regard to outlets and networks based on conductive media such as wires and cables, it will be appreciated that such outlets are equally applicable in the case wherein the network medium is non-conductive, such as fiber-optical cabling. Active outlets supporting data interfaces and based on fiber optic cabling are described in U.S. Patent Application US 2002/0146207 Published Oct., 10 2002 to Chu, entitled `Fiber Converter Faceplate Outlet`, as well as in U.S. Pat. No. 6,108,331 to Thompson entitled `Single Medium Wiring Scheme for Multiple Signal Distribution in Building and Access Port Therefor`. As such, the term `wiring` as used in this application as well as in the appended claims should be interpreted to include networks based on non-conductive media such as fiber-optics cabling.

While the outlets described above use active circuitry for splitting the data and service signals, passive implementations are also available. An example of such a passive outlet is disclosed in WO 02/25920 to Binder entitled `Telephone communication system and method over local area network wiring`. Such outlets are available as part of the etherSPLIT system from QLynk Communication Inc. of College Station, Tex. USA. etherSPLIT is a registered trademark of Dynamic Information Systems.

The described above outlets are complete and self-contained devices. As such, they can be easily installed in new houses instead of regular passive simple outlets. However, such solutions are not appropriate in the case of retrofitting existing wiring systems. In most cases, any such modification will require dismantling the existing outlets and installing the new ones having the improved features. Such activity is cumbersome, expensive and will often require professional skill. Furthermore, owing to safety aspects involved while handling hazardous voltages (such as in the powerlines and telephone lines), local regulations may require only certified personnel to handle the wiring, making it expensive and militating against a do-it-yourself approach.

Furthermore, as the technology and environment change in time, a need to upgrade, modify or change the outlet functionalities, features and characteristics may arise. For example, the data interface may need to be upgraded to interconnect with new standards. In another example, the circuitry may need to be upgraded to support higher bandwidth. Similarly, management and Quality of Service (QoS) functionalities may need to be either introduced or upgraded. In yet other examples, additional functionalities and interfaces may need to be added. Using complete self-contained outlets as a substitute to the existing ones also introduces the disadvantages described above.

Plug-in Device.

One approach to adding functionality to existing outlets is by using a plug-in module. Such plug-in modules are described in US Patent Application US 2002/0039388 to Smart et al entitled `High data-rate powerline network system and method`, US Patent Application US 2002/0060617 to Walbeck et al. entitled `Modular power line network adapter` and also in US Patent Application US 2003/0062990 to Schaeffer, J R et al. entitled `Powerline bridge apparatus`. Such a module using HomePlug.TM. technology are available from multiple sources such as part of PlugLink.TM. products by Asoka USA Corporation of San Carlos, Calif., USA. HomePlug is a trademark of HomePlug Powerline Alliance, Inc. of San Ramon, Calif., USA. Various types of snap-on devices are also described in WO 04/001034.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a transmission line characteristic impedance is measured by applying regular lumped impedance/resistance measuring. Any other lumped or distributed impedance/resistance measuring technique known in the art may be equally applied. In one aspect of the invention the measurement is based on transmitting, sourcing or exciting an electrical signal, either voltage or current (or both). In one aspect of the invention the measurement is based on exciting a known energy into the transmission-line, and measuring the current flow to the transmission line directly or indirectly such as using voltage divider. The measured values are used to calculate the transmission-line characteristic impedance. Measuring the characteristic impedance may be initiated periodically, upon receiving an external electrical signal (e.g. from another system), upon manually applying a signal, or upon powering up, or upon sensing any other signal excitation such as packet or session as part of a data communication session.

In order to allow proper measurement, no other signals (such as reflections or data communication signals) should exist and affect the measurement. According to one aspect of the invention, the impedance (either lumped or distributed) measuring is executed shortly after injecting the measurement signal into the transmission-line, and prior to reflections arrival from taps or non-terminated ends to the measured transmission line end. Since practically transmission-lines are not homogenous and do not have infinite length, reflections from taps, non-homogenous points or non-terminated remote ends occur and will arrive to the measured end. Thus, the measurement should be executed and completed shortly after applying the measurement signal, before the reflections arrive to this line end. In order to make any subsequent use of the measured value, the calculated characteristic impedance (or any function thereof such as the voltage/current measured) should be stored.

According to one aspect of the invention the transmission-line serves as a medium for data communication. In such configuration, a modem (being transmitter, receiver, transceiver or the like) is connected to a point along the transmission-line as well as to the transmission-line end-point relating to the impedance measurement. Characteristic impedance measurement may be used to determine whether a termination is required in a specific connection point. According to one aspect of the invention the termination value is determined according to the measured characteristic impedance. For example, the termination value can be set to be equal to the measured lumped impedance in order to minimize reflection in an end-point. In the case wherein data communication is involved over the same transmission-line, time domain multiplexing is used to allow both the modem and the measurement to share the transmission line, wherein the modem operation should be halted during the impedance measurement, in order not to interfere with the measurement and to enable proper and accurate measurement. According to one aspect of the invention, this is achieved by disconnecting the modem (to include transceiver and transmitter) from the transmission-line during the measurement phase, and re-connecting it after the measurement is completed. As such, the system may be exclusively in either a measurement state or a data communication state.

According to one aspect of the invention, a frequency division multiplexing (FDM) approach is applied in order to concurrently carry both an application signal (such as data communication signal) and an impedance measurement related signal over the transmission-line. In this arrangement, the measurement system uses a signal carried in one or more frequency bands distinct from the band wherein the application signal is carried. The characteristic impedance of the transmission-line in the frequency band or bands not being part of the measurement system may be approximated using known extrapolation or interpolation techniques.

According to one aspect of the invention, the measured/calculated transmission-line characteristic impedance is used for estimating the count of wire pairs connected to a single connection point, for use with one or more similar wire pairs having similar nominal characteristic impedance Z0 and all connected to the single connection point. By instantaneously measuring the connection point lumped impedance Z, the connected wire pairs count can be estimated to be Z0/Z. The estimated pairs count may be visually indicated to a user as part of a pairs count test-set.

According to one aspect of the invention, the pair count is used to identify the end point of an unknown wiring structure. In the case wherein Z=Z0, a single wire pair connection-point is detected, thus requiring a termination to be connected to this point in order to minimize reflections from this wire-pair end-point.

According to one aspect of the invention in-wall hidden wire-pairs are measured. Such wire pairs may comprise telephone, AC power or CATV wiring infrastructure, as well as any other wiring. The wire pair may be carrying service signals (such as telephone, AC power or CATV signals), and may be accessed via outlets (such as telephone, AC power or CATV outlets). In the case wherein outlets are used to connect to the wiring, the impedance measuring or the termination setting or both circuits may be integrated (in part or in full) into the outlet.

According to one aspect of the invention for use with a transmission-line carrying a signal and having a nominal characteristic impedance and terminated with a impedance-controlled termination, the proper termination value (having the same value as the nominal characteristic impedance) is matched to the transmission-line by using a closed control loop, wherein the power dissipated by the impedance-controlled termination (connected to the transmission-line) is measured and used for changing the impedance-controlled termination value to obtain a maximum power dissipation. The power dissipation by the termination can be measured directly by sensing the voltage across or the current flowing through the termination. Alternatively, the dissipated power is indirectly measured by measuring a physical phenomena affected by the dissipated power (e.g. heat).

The measuring system (in whole or in part) may be enclosed as a stand-alone unit, housed/integrated as part of a modem, or housed in integrated form as part of a service outlet or as a snap-on module. Similarly, the termination setting system (in whole or in part) may be stand-alone, or housed/integrated as part of a modem, or housed in integrated form as part of a service outlet, or as a snap-on module

The above summary is not an exhaustive list of all aspects of the present invention. Indeed, the inventor contemplates that his invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the detailed description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary.

It is understood that other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein are shown and described only embodiments of the invention by way of illustration. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modification in various other respects, all without departing from the scope of the present invention as defined by the claims. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of non-limiting example only, with reference to the accompanying drawings, wherein like designations denote like elements.

FIG. 1 illustrates schematically a point-to-point network.

FIG. 1a illustrates schematically a multi-point network.

FIG. 2 illustrates schematically a multi-point network with a tap.

FIG. 3 illustrates schematically a general functional block diagram of an exemplary Characteristic Impedance Meter (CIM) according to the invention.

FIG. 4 illustrates schematically a general functional block diagram of an exemplary termination system according to the invention.

FIG. 5 illustrates schematically a general functional block diagram of an exemplary Characteristic Impedance Meter (CIM) according to the invention.

FIG. 6 illustrates schematically a general functional block diagram of an exemplary Voltage controlled Resistor (VCR).

FIG. 7 illustrates schematically a general functional flow chart of an exemplary operation according to the invention.

FIG. 8a illustrates schematically a general termination system.

FIG. 8b illustrates schematically a general functional block diagram of an exemplary termination system according to the invention.

FIG. 9 illustrates schematically a general functional block diagram of an exemplary pairs counting system according to the invention.

FIG. 10 illustrates schematically a frequency bands allocation scheme according to the invention.

FIG. 11 illustrates schematically a general functional block diagram of an exemplary termination system according to the invention.

FIG. 12 illustrates schematically a graph of a dissipated power versus a termination resistance.

FIG. 13 illustrates schematically a telephone-wiring infrastructure in a house.

FIG. 14 illustrates schematically an AC-power wiring infrastructure in a house.

FIG. 15 illustrates schematically an exemplary termination test-set according to the invention.

FIG. 16 illustrates schematically an exemplary AC power wiring termination device according to the invention.

FIG. 17 illustrates schematically a typical packet structure.

FIG. 18 illustrates schematically a general functional block diagram of an exemplary termination system according to the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The principles and operation of a network according to the present invention may be understood with reference to the drawings and the accompanying description wherein similar components appearing in different figures are denoted by identical reference numerals. The drawings and descriptions are conceptual only. In actual practice, a single component can implement one or more functions; alternatively, each function can be implemented by a plurality of components and circuits. In the drawings and descriptions, identical reference numerals indicate those components that are common to different embodiments or configurations.

A part of one embodiment according to the present invention is shown as Characteristic Impedance Meter (CIM) 30 in FIG. 3. The CIM measures the characteristic impedance of a transmission line by applying a signal to the line, and directly measuring the input impedance into the transmission line by means of voltage division shortly afterwards. The CIM 30 measures the characteristic impedance of the Transmission line Under Test (T.U.T or TUT) 42 connected via port 39, and having an unknown characteristic impedance Z0. The measurement sequence starts upon sensing a MEASURE signal in port 31, signaling the CIM to start the measurement process. The MEASURE signal at port 31 is fed to pulse generator 32, which outputs a pulse shown as square wave pulse signal 33. The pulse signal waveform 33 starts at time T0, is .tau. seconds long and has an amplitude of V' volts. In the case wherein the characteristic impedance is required to be measured in a specific and/or limited frequency band, the pulse signal is then fed to a band-pass filter 34 limiting the signal energy to the required band. If the signal is generated having the frequency spectrum required, and/or if no frequency band limitations exists, such a filter 34 may be omitted. After being filtered by the filter 34, the pulse is connected to the TUT 42 via the series resistor Rs 36 connected to the port 39. The processing unit 37 is considered to have very high input impedance, hence does not interfere with the signal. The voltage at port 39 (and at the input to the processing unit 37) is as such a voltage formed by dividing V' between the resistor Rs and Z0 (pure resistive characteristic impedance is assumed). As such, the divided voltage Vd at port 39 is: Vd=V'*Z0/(Rs+Z0), assuming no attenuation by the filter 34. In the case of amplitude attenuation by the filter 34, the voltage V' reflects the amplitude at the filter 34 output. Since V' and Rs are known, the voltage Vd at port 39 is a direct function of the value of the characteristic impedance Z0. In order to allow for accurate measurement, the value of resistor Rs should be as close as possible, or at least of the same order of magnitude, as the measured impedance Z0. The voltage Vd is fed to the processing unit 37, which provides a signal output which is a function of the voltage at port 39. For example, the processing unit 37 may provide a voltage proportional to the Vd above. In another example, the processing unit 37 calculates Z0 by the equation Z0=Rs*Vd/(V'-Vd), and provides a signal (e.g. voltage) proportional to the Z0 calculated. Other transfer functions may also be considered. If processing is not required, processing unit 37 may be omitted. Assuming a practical and finite length TUT, the pulse signal starts to propagate along the transmission line, and assuming taps, non-terminated ends or any other non-continuities, a reflection signal will appear at port 39, causing the measured Vd to be inaccurate and not to reflect the actual voltage division discussed. As such, an accurate value of Vd exists at port 39 only for a short period after the pulse signal start (T0). Hence, there is a need to latch and store the value at this instant.

The pulse signal 33 is also provided to a delay unit 35. After a predetermined delay period (after T0), a signal is output to the trigger input of a sample and hold unit 38, which latches and holds the signal output from processing unit 37 as signal Vm at port 41. Hence, signal Vm (e.g. voltage) represents a function of the TUT characteristic impedance Z0. The delay value should not be too short, in order to allow an accurate and fully stabilized value. On the other hand, the delay value should not be too long in order to obviate the effect of reflections. The value of .tau. should be small enough in order not to occupy the transmission line for long and to minimize the period required for the measurement. Similarly, the value of .tau. should be long enough to allow accurate and stabilize measurement. In a system that has been built and tested, a pulse of .tau.=15 nanoseconds enabled accurate reflection-free measurement of any twisted-pair cable longer than 70 centimeters.

Hence, a known while after a MEASURE signal is sensed in port 31, the CIM will output in port 41 a signal which represents the value of the characteristic impedance Z0 of the TUT 42 connected in port 39.

The CIM 30 above is operative to measure the characteristic impedance of the TUT 42. After such measurement is performed, adequate termination should be provided based on the measured value. A system 40 providing both measurement and setting of the required termination value is shown in FIG. 4. The TUT 42 shown in the figure is connected via a switch 44, having two distinct states, designated as M (Measurement) and S (Setting), the states being selected by a control signal line SELECT 49. In measurement (M) state, the TUT 42 is connected to the CIM 30 port 39, as described in FIG. 3 above. In such a state, upon application of a MEASURE signal to port 31 of the CIM 30, the CIM 30 will perform the measuremen