Abstract:
A method of distributing wide band data using a neutral-to-ground circuit within an electrical wiring installation includes modifying a load center with an interface module which interfaces to the neutral-to-ground circuit and configuring the interface module to compensate for varying impedance within the neutral-to-ground circuit to improve data transmission characteristics. Multiple embodiments are included within the method for compensation of varying impedance including channel sounding, spectral waterfilling, and communications using spread spectrum techniques, for example, frequency hopping and direct sequencing techniques.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to data transmission and more specifically to high speed data distribution over residential electrical wiring. 
   High speed transmission of data throughout a residence facilitates performing home automation functions such as home security and appliance controls. Residential electrical systems can be used for data communication within a residence. For existing residences, wiring in the residential electrical systems is advantageous to use because, in most instances, use of such wiring facilitates installation of a communication system. 
   The installation of dedicated data wiring is one alternative to the use of the residential electrical system, for data communication, but is undesirable due to cost and other factors. The other factors include the invasiveness of dedicated data wire installation in existing structures either requiring unsightly installations along baseboards, ceilings, and walls or damage and repair to walls when attempting to install behind existing wallboard or plaster walls. 
   Data can be transmitted over residential electrical wiring using a neutral-to-ground circuit of the residential wiring system. Using neutral-to-ground circuits for the transmission of data within a residence has advantages over line-to-ground or line-to-neutral circuits since the voltage present on the line circuit is avoided. However, neutral-to-ground data transmission is also complicated, as is line-to-ground or line-to-neutral data transmission in that the impedance of the circuit changes as devices are plugged into the circuit. Therefore impedances encountered by a data transceiver is constantly changing. The changing impedance affects the nature of optimal signaling techniques and also affects the bandwidth or data carrying capacity of the data transceivers. 
   It would be desirable to be able to periodically diagnose the impedance of the neutral-to-ground circuit and compensate for detected impedance changes thereby enabling the circuit to maintain a wide data bandwidth thus providing a reliable high-speed data transmission medium which is available to most existing homes and eliminates the cost involved with installation of dedicated data wiring. 
   BRIEF SUMMARY OF THE INVENTION 
   In an exemplary embodiment, a method of distributing wide band data using a neutral-to-ground circuit includes modifying a load center with an interface module configured to interface with the neutral-to-ground circuit and configuring the interface module to compensate for varying impedance within the neutral-to-ground circuit. 
   A circuit breaker box within a residence is one example of a load center. The interface module is configured to compensate for varying impedance within the neutral-to-ground circuit by coupling an impedance to the circuit to improve data transmission characteristics. The coupled impedance within the interface module can be varied to maintain the data transmission characteristics as the impedance of the neutral-to-ground circuit changes. The interface module also serves as the interface for the transmission and reception of data along the neutral-to-ground circuit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of a residential wiring circuit including a load center; 
       FIG. 2  is a schematic diagram of a residential wiring circuit including components of a high speed data transmission system; and 
       FIG. 3  is a block diagram of an interface module configured to adjust impedance of a neutral-to-ground circuit. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a schematic diagram  10  of a residential wiring circuit. Typically, a supply of power is routed from an electric supplier, either underground or otherwise, and is connected to a customers residence or business at an electric meter  12  at which point the electric wiring enter the customers residence. Inside the residence, there is typically a load center  14 , which may also be called a fuse box or a breaker box, at which point the electric supply is divided into individual circuits for distribution throughout the residence. The electric supply is divided at breakers  16  and distributed throughout the residence to electrical outlets  18 . While  FIG. 1  is a simplified diagram, electrical distribution throughout a residence is based on use. A circuit to an oven, for example, may be one individual circuit, while multiple wall outlets to one or more bedrooms, may be another individual circuit. Most electrical systems are of three wire design which are designated individually as line  20 , neutral  22  and ground  24 . In most installations, neutral  22  and ground  24  are electrically connected, or “tied together” within load center  14 . As the separate neutral  22  and ground  24  wires are routed from load center  14  throughout the residence, an impedance can be found between neutral  22  and ground  24  due to the long lengths of wire needed to wire a residence for electricity and due to the loading of the individual circuits with lighting, appliances, televisions, computers and the like. 
     FIG. 2  is a schematic diagram of a residential wiring circuit  30  including one embodiment of a high speed data transmission system. Components in circuit  30 , identical to components of diagram  10  (shown in FIG.  1 ), are identified in  FIG. 2  using the same reference numerals as used in FIG.  1 . In addition, there is included in  FIG. 2  an interface module  32 , a data transceiver/external controller  34 , a data dependent device  36  which is configured for communication along the neutral-to-ground circuit with controller  34 , and a transceiver  38  which is also configured for communication along the neutral-to-ground circuit with controller  34 . In one embodiment, and as shown in  FIG. 2 , interface module  32  is physically located within load center  14 . Alternatively, interface module  32  is located external to load center  14 . 
   Interface module  32  is configured to compensate for varying impedance within the neutral-to-ground circuit. In one embodiment, interface module  32  assesses a data rate capacity of the neutral-to-ground circuit as a data channel and establishes a signaling rate. Assessment of data rate capacity may include determining the impedance of the neutral-to-ground circuit data channel as a function of frequency using methods described below. 
     FIG. 3  is a block diagram of interface module  32  configured to determine and adjust the impedance of a neutral-to-ground circuit within a residence according to one embodiment of the present invention. Interface module  32  includes a coupler  52  which couples to the neutral-to-ground circuit for the transmission and reception of data. In one embodiment, coupler  52  is an isolation transformer. In another embodiment, coupler  52  is a capacitive coupling device. Other embodiments of coupler  52  exist which include any device configured to transfer signal data onto the neutral-to-ground circuit. 
   Interface module  32  further includes a modulator/demodulator  54  for formatting transmitted and received data. In one embodiment, modulator/demodulator  54  includes a voltage controlled oscillator (not shown) which creates a signaling waveform capable of being transmitted on the neutral-to-ground circuit. In another embodiment, a comb filter (not shown), which converts a received signal into a set of orthogonal components, demodulates data received from the neutral-to-ground circuit for external processing. However modulator/demodulator  54  includes other devices which are capable of creating and receiving signaling waveforms, for data transmission and reception protocols, for example, CE Bus and RS-232. 
   Interface module  32  also includes a sounder  56  which is configured to generate short pulses or impulses for transmission onto the neutral-to-ground circuit, as described above. Sounder  56  further receives an impulse response from the neutral-to-ground circuit from which transmission characteristics of the neutral-to-ground circuit can be ascertained, based upon a spectrum of the response compared to a spectrum of the transmitted impulse. A calculation device  58  within interface module  32  is configured to determine an amount of impedance to be added or subtracted from the neutral-to-ground circuit based upon the response to the impulse received as compared to the impulse generated by sounder  56 . In one embodiment, calculation device  58  is microprocessor based and configured to execute a program which determines the required impedance on the neutral-to-ground circuit based upon the impulse response described above. 
   A variable or fixed impedance  60  includes both resistive and reactive loads which are applied across the neutral-to-ground circuit based upon commands received from calculation device  58 . An interface  62  to external controller  34 , (shown in  FIG. 2 ) which includes an input/output (I/O) signaling port  64  and an input/output (I/O) data port  66 . I/O data port  66  serves as the data interface to external controller  34 . I/O signaling port  64  is a port to calculation device  58 . Through I/O signaling port  64 , external controller  34  communicates to interface module  32  the desired data transmission rates along the neutral-to-ground circuit and initiates operation of interface module  32  as above described. I/O signaling port  64  also is the port which transmits back to external controller  34  the data rate capacity of the neutral-to-ground circuit, based upon impulse response characteristics and applied impedance as calculated by calculation device  58 . 
   One method of determining transmission characteristics and therefore impedance of the neutral-to-ground circuit data channel using interface module  32  as described above, includes sounder  56  signaling modulator/demodulator  54 , based upon commands from calculation device  58 , to send a short pulse having a spectral occupancy equal to the highest signaling bandwidth available to modulator/demodulator  54  onto the neutral-to-ground circuit data channel via coupler  52 . The method continues by sampling the pulse with transceiver  38  (shown in FIG.  2 ), computing the power spectral density of the short pulse at the transceiver and reporting the spectral coefficients back to interface module  32  using a low rate conventional, signaling scheme. The reported spectral coefficients are used by calculation device  58  to determine impedance of the neutral-to-ground circuit. 
   Another method of determining impedance of the neutral-to-ground circuit using interface module  32  is to transmit the short pulse as described above onto and along the neutral-to-ground circuit to transceiver  38 . Transceiver  38  is configured to receive the transmitted pulse and to transmit the pulse as received back to interface module  32  along the neutral-to-ground circuit. Interface module  32  is configured to then process the signal received back from transceiver  38  with calculation device  58  to determine the impedance of the neutral-to-ground circuit. Such a determination is made based upon changes within the components of the original transmitted pulse, for example, certain frequency elements from the pulse may be lost due to impedance characteristics of the neutral-to-ground circuit. 
   After a determination of impedance the neutral-to-ground circuit, interface module  32  is configured to determine if the neutral-to-ground circuit will support data transport at the rate requested by external controller  34 . Calculation device  58  is configured to compensate for varying impedance within the neutral-to-ground circuit by adjusting variable impedance  60  to a value which improves the neutral-to-ground circuits impedance characteristics as a data carrier. One such method for adjusting impedance for improvement in reliability of data transmission is known in the art as hill climbing. 
   Interface module  32  is configurable to hill climb which is best described as a technique for optimizing a multi-input function by maximizing a complicated, non-linear function based on a selection of the multiple input variables. In one embodiment, interface module  32  is configured to choose, arbitrarily if necessary, an initial set of input values for a function, which are impedances based on a set of adjustable discrete elements, such as resistors, capacitors and inductors within variable impedance  60 . The function is evaluated based upon impedances selected as the input for the function and the function output value is saved. The function output value is termed known value. 
   The inputs to the function are then perturbed, randomly or deterministically, singly or in a plurality, and the function&#39;s value computed or measured for the new set of values of the input impedances. If the function is closer to a desired value over its previously known value, the new set of input variables is adopted as the new set of preferred input impedances and the new value of the function becomes the new known value. 
   The perturbation to the input variables that results in a new known value is regarded as a hill climbing direction and this direction is searched for a local maximum of the known value. For variable impedance  60 , such a value can be complex impedance, amplitude and phase over a wide bandwidth. The local maximum search may be done by any of a suite of well-known techniques such as a bisection search or a least squares fit between a frequency dependent impedance curve and a desired impedance curve over a spectrum of interest. 
   Once a local maximum has been determined, a new hill climbing direction is chosen, randomly or deterministically, and the process is repeated. The hill climbing approach continues until a limit on computing time, a number of iterations or other limiting factors are reached. 
   One method of adjusting a variable impedance  60  within interface module  32  to improve data transmission characteristics includes spectral waterfilling, which is the spectral matching of the signaling waveform to the neutral-to-ground circuit data channels spectral transfer function. Noise power spectral density on the data channel is estimated and measured channel impedance transfer function appropriately adjusted before waterfilling. 
   Calculation device  58  can alternatively determine a maximum signaling rate, or data rate, the present impedance of the neutral-to-ground will support and pass that information to external controller  34 . 
   In one alternative embodiment, a fixed impedance can be introduced onto the neutral-to-ground circuit. Interface module  32  is configurable to compensate for varying impedance in the neutral-to-ground circuit by switching in a fixed impedance  60  within interface module  32  that configures the neutral-to-ground circuit to accommodate numerous communication carriers or bands of communications frequencies. 
   While the methods and devices described herein refer to residential wiring and data transmission, residential is but one example of such an application of the embodiments herein described and the embodiments should not be construed to be so limited. The embodiments herein described are equally applicable to other applications including, but not limited to, commercial, industrial and any other installation of electrical wiring. In addition, supported data transmission protocols are not specifically described within the embodiments. Any communications protocol can be adapted or bridged to the power line neutral-to-ground circuit. For example, ethernet communications is bridged to the neutral-to-ground circuit using a gateway device such as a computer with a power line modem. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.