Apparatus and method for communication over power lines

An apparatus and method are provided for communicating over power lines. The apparatus includes a coupling modem that is situated between a power line and a device. The coupling modem is configured to demodulate a signal received from the power line into a sine signal and a cosine signal. The coupling modem is also configured to modulate a communicated bit stream received from the device into a transmitted signal in order to impose the transmitted signal onto the power line.

FIELD

The present invention relates to an apparatus and method for communicating data over a pre-existing power line.

BACKGROUND

Sensors and instrumentation are needed to monitor processes of systems strung along power lines that supply current to those systems. Examples of such systems include In-Situ Health Monitoring and communication within and amongst individual solar cell subpanels within a power producing solar array on earth, in orbit, or in deep space and on other celestial bodies.

SUMMARY

Certain embodiments of the present invention may provide solutions to the problems and needs in the art that have not yet been fully identified, appreciated, or solved by current systems that transmit and receive data over power lines.

For instance, a modulator/demodulator (modem) can be placed between an output and an input of a serial device, such as a universal or asynchronous receiver and/or transmitter (UART), or can replace a line driver for a controller area network (CAN) transceiver using existing power lines. This allows for a more robust and easily expandable system by taking advantage of the existing power lines that feed other devices.

In accordance with an embodiment of the present invention, an apparatus is provided. The apparatus includes a coupling modem that is situated between a power line and a device. The coupling modem is configured to demodulate a signal received from the power line into a sine and a cosine signal, and configured to modulate a signal received from the device onto the power line.

In accordance with another embodiment of the present invention, a method is provided. The method includes demodulating a signal received from the power line into a sine and a cosine signal and modulating a signal received from the device onto the power line.

In accordance with yet another embodiment of the present invention, an apparatus is provided. The apparatus includes a demodulator that is configured to receive a signal from a power line and demodulate the signal into a sine signal and a cosine signal using a quadrature clock. The apparatus also includes a modulator that is configured to receive a bit stream of data and a clock signal to generate a transmission signal for transmission onto the power line.

DETAILED DESCRIPTION OF THE EMBODIMENTS

It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of an apparatus, a system, a method, and a computer readable medium, as represented in the attached figures, is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention.

Embodiments of the present invention pertain to an apparatus and method for communicating over power lines. For instance, the apparatus and method provide for an effective modulation and asynchronous demodulation of on-off-keyed (OOK) bit streams from a serial device onto and off of power lines. In other words, the apparatus may include a modem that can be placed between an output and input of a serial device (e.g., a universal asynchronous receiver/transmitter (UART)) or replace a line driver for a controller area network (CAN) transceiver. This allows for a more robust and easily expandable system by taking advantage of existing power lines on a target system. Because existing power lines are utilized, electronic components that require communication can be added to the target system without the need to add additional wiring for communications.

Because OOK modulation is generally the simplest form of amplitude shift keying (ASK), the embodiments of the present invention can also be applied to systems using ASK and non-ASK systems such as phase shift keyed (PSK) devices. In some embodiments, logic zeros (0) are used in the OOK bit stream as a frequency burst and transmit logic ones (1) for an absence of a burst (no signal). In this manner, this apparatus can, as previously mentioned, replace the physical layer of a CAN system.

In another embodiment, the apparatus may use, instead of electrical impulses imparted onto a power line, sonic energy (such as for an underwater application using communications analogous to sonar, or sound through ground or air) or for an in vitro device for medical applications such as intercommunication between implanted neuroprosthetic devices, etc.

In other embodiments, the apparatus may use optical transmission and can be operated using an optical fiber as the communications backbone and light emitting diodes (LED) or laser diodes and photodetectors as the output/input devices. Or, the apparatus can operate simply using light emitting diodes and photodetectors with transmission through the air. A person of ordinary skill in the art will appreciate that modulation/demodulation over a laser in air is possible.

Since the modulation frequency is selectable, and since discrimination is high, the apparatus can easily be used to execute frequency-hopping algorithms and allow for the simultaneous operation of multiple networks operating at different carrier clock frequencies on the same power line.

FIG. 1illustrates an apparatus100for communication over power lines, in accordance with an embodiment of the present invention.

Apparatus100includes, but is not limited to, a filter102, a coupling modem104, a signal averaging unit106, an absolute value unit108, a magnitude unit110, a discriminator/automatic gain control (AGC) unit112, a hot power line and a neutral power line. In one or more embodiments, the hot power line is configured to power a host device (not shown) and communicate data (e.g., transmit and receive a bit stream) to and from the host device.

Filter102is operatively connected to the hot and neutral power lines and a power device114. Power device114may provide power to signal averaging unit106, absolute value unit108, and magnitude unit110. Filter102conditions (or regulates) power for power device114and functions as impedance to the transmitted and received data signals. In other embodiments, depending on the system's configuration, filter102may be an all pass device, or may be a wire inductance device, voltage regulator, etc.

Coupling modem104is operatively connected to the hot power line, signal averaging unit106and the host device. Coupling modem104is configured to modulate data signals received from the host device and demodulate data signals received from the hot power line.FIGS. 2 and 3illustrates two different embodiments of coupling modem104to demodulate the data signals received from the hot power line, andFIG. 4illustrates an embodiment of coupling modem104to modulate the data signals received from the host device.

In this embodiment, an incoming (or received) data signal is capacitively coupled to the modem. When an outgoing (or transmitted) data signal is driven in a push-pull fashion, capacitive coupling can be utilized. When the outgoing signal is single ended, i.e., a simple open collector/open drain output, then resistive coupling can be utilized. Resistive coupling is utilized for high temperatures, where push-pull topographies may be nonexistent.

It should be appreciated that depending on the configuration of apparatus100, a band limiting or rate limiting filter may be used between the coupling element and the modem to block interference from other signals on the power lines. Preamplification may also be desirable in such instances. It should also be noted that the coupling modem104is sectioned to realize modulation for transmission and demodulation for reception of the communicated data signals. For example, coupling modem104includes a demodulator and a modulator. See, for example,FIGS. 2-4.

Signal averaging unit106receives the demodulated signals (e.g., Rx Signal OUT sine and Rx Signal OUT cosine) from coupling modem104to average the demodulated signals. For instance, signal averaging unit104is configured to compute the average of the Rx Signal OUT sine and Rx Signal OUT cosine to create a direct current (DC) value or signal. In other words, the demodulator described below and signal averaging unit106are configured to pass frequencies at the sine and cosine clock frequencies and block frequencies that are not at the sine and cosine clock frequencies.

For example, in signal averaging unit106, an alternating current (AC) signal carrier with average peak magnitude m in phase with the sine component can be completely out of phase with the cosine clock. As a result, the output of the sine component of the demodulator may yield a positive pulse train with average value m and the cosine component may produce a zero signal. However, an AC signal carrier with average peak magnitude m that is 180° out of phase with the sine component may also be completely out of phase with the cosine clock. Thus, the output of the sine component of the demodulator may yield a negative pulse train with average value −m (or a magnitude of m) and the cosine may produce a zero signal.

It should be appreciated that input signals at all other phase relationships can share energy between the sine and cosine components of the demodulator and, after averaging, the sums of their absolute values can equal and have a magnitude of m. As a result, the incoming signal can be discriminated. All signals of frequencies greater than or less than the clock frequency can appear at the outputs of the sine and cosine components of the demodulator to have magnitudes of zero. However, the speed at which the signals go to zero as a function of frequency difference from the clock frequency is dependent on the quality factor of signal averaging unit106.

In other words, signal averaging unit106, as shown inFIG. 1, has a high discrimination and maps the incoming frequency of interest to DC. This feature allows for multiple nets running at different frequencies to operate simultaneously on the same power line without interference. In other embodiments, signal averaging unit106may be a single resistor/capacitor, low pass circuit, or a high order band pass filter, which may be continuous or clocked.

It should be noted that the relationship between the two signals reveals phase information, and if the phase of the input signal abruptly changes, as in PSK, then this transition in phase is evident at this stage. Also, the above function may be realized in a discrete space through the use of an analog to digital conversion and subsequent digital signal processing.

Absolute value unit108receives the output signals from signal averaging unit106and calculates the absolute value of the signals. This function may be calculated in a number of ways in hardware and/or software, e.g., a precision rectifier. In other embodiments, absolute value unit108may be composed of diode based operational amplifiers and saturable operational amplifiers with no diodes.

Once the absolute values of the two signals (e.g., sine and cosine) are determined, the two signals are summed in an adder circuit (e.g., magnitude unit110) to create a DC output with magnitude m for an alternating current (AC) input signal at the same frequency as the clock signal of average peak magnitude m.

This is the technique used in a fully analog processing front end. The above function may be realized entirely in a discrete space through the use of analog to digital conversion and subsequent digital signal processing. In this embodiment, magnitude calculations have been implemented to include
Magnitude=MAX {A,B}{A,B}(Eq. 1)
Magnitude=MAX {A,B}+0.5×MIN {A,B}(Eq. 2)
Magnitude=√{square root over (A2+B2)}(Eq.3)
Magnitude=A+B(Eq. 4)where A is the absolute value of the average of the sine signal, and B is the absolute value of the average of the cosine signal. It should be appreciated that while each of the above magnitude calculations can be utilized, they do not represent an exhaustive set of possible magnitude calculations.

One of ordinary skill in the art will appreciate that in the case of transmitted zeros (dominant low), the output of magnitude unit108is m for a transmitted zero, and is near 0 (ground) for a transmitted one.

Discriminator/AGC unit112receives the DC output with magnitude m from magnitude unit108. Discriminator/AGC unit112includes a comparator circuit that outputs a low when the input is greater than m/2. When the input is lower than m/2, discriminator/ACG unit112outputs a high. Hysteresis is indicated within the comparator circuit to reduce uncertainty and improve response. This allows the input signal to be converted to a bit stream of data, or received data.

Determining the threshold for the discriminator, that is, the value that the discriminator's input is compared to, may be performed manually or determined a priori through experimentation. The value can be automatically generated based on statistics on the incoming signal peak values. For instance, when the discriminator threshold value is fixed, the AGC analyzes the peak values of the incoming signal and adjusts a gain stage to amplify the signal from the magnitude calculator to a peak value about two times the threshold.

FIG. 2illustrates a demodulator200for demodulating a received signal, in accordance with an embodiment of the present invention. Demodulator200, which may be a coupling demodulator, includes a plurality of resistors R and a switch S, where plurality of resistors R are equal. Coupling demodulator200receives a signal at an input (Rx Signal In) and demodulates the received signal using a clock cycle. Because coupling demodulator200uses asynchronous demodulation, two square waves of a quadrature clock are used at the frequency of interest. For instance, depending on the quadrature clock (i.e., two clock streams that are 90 degrees out of phase with a 50 percent duty cycle), the received signal is outputted in its native form or inverted form. When switch S is open, the signal is multiplied by +1 at the frequency of interest, thus allowing the signal to pass through. However, when the switch is closed, the signal is multiplied by −1 at the frequency of interest, thus allowing the signal to be inverted.

FIG. 3illustrates a demodulator300for demodulating a received signal, in accordance with an embodiment of the present invention. In this embodiment, coupling demodulator300includes a plurality of resistors R and a switch S. In this embodiment, when switch S is open, the signal is multiplied by +1 at the frequency of interest, thus allowing the signal to pass through. However, when the switch is closed, the signal is multiplied by −1 at the frequency of interest, thus allowing the signal to be inverted.

In some embodiments, separate clocks for sine and cosine are supplied by the application, though a single clock can be provided and, at the modem, the single clock can be converted into separate sine and cosine components through various means. The clocks can have a frequency many times greater than the baud rate of the communications bit stream. Stated another way, multiple cycles of the clock can occur for one bit period of the data. For example, 8 cycles of the clock can transition during one bit of data that is being transmitted.

FIGS. 2 and 3illustrate two possible demodulators to implement the multiplication of the input signal with the sine (0°) and cosine)(90°) square waves. Regardless of which demodulator is being utilized, for one state of clock in, Rx Signal Out=Rx Signal In, while for the other state, Rx Signal Out=−Rx Signal In, with the plurality of resistors R being equal.

It should be appreciated that the demodulators are not limited to the circuits shownFIGS. 2 and 3, but there may be other demodulators as would be readily appreciated by a person of ordinary skill in the art. Regardless of the circuitry, one circuit can be used for the sine (0°) component and another circuit can be used for the cosine (90°) component to yield two outputs from coupling modem104, as shown inFIG. 1.

In an alternative embodiment, the above function may be realized entirely in a discrete space through the use of an analog-to-digital conversion and subsequent digital signal processing.

FIG. 4illustrates a modulator400for modulating a transmitted signal onto a power line, in accordance with an embodiment of the present invention. Modulator400is configured to receive a communicated bit stream along with a clock signal and transform the communicated bit stream into a transmitted signal that can then be imposed on the power line. The transmitted communication bit stream signal may be generated by gating a clock frequency (e.g., a sine or cosine signal) with the actual bit stream. The resulting OOK signal can then be imparted onto the power line using the coupling technique described below.

InFIG. 4, the gate402represents a DeMorgan equivalent of a NOR gate with inverters404. During a low state of a transmitted signal at input (Tx Signal In), the transmitted signal at output (Tx Signal Out) can toggle at the rate of the clock, such that the Tx Signal Out can be high when the clock is 0 and can be low when the clock is 1. For example, for Tx Signal In, the digital bit stream can have a 0 value as its current, and the clock can have a period much shorter than the period of a bit of data. It should be noted that the clock is imposed onto the power line for one state of the signal and suppressed for the other state of the signal. Also, the signal is the gate for the clock to be imposed onto the power line.

It should also be appreciated that the clock need not be inverted by this function (e.g., inversion function at input) nor does the Tx Signal Out have to be positive with respect to the input conditions. If a dominant low is not desired at the output, then inverter404, which inverts Tx Signal In, may be removed from the logic.

In an alternative embodiment, if the above gate402was replaced by an exclusive OR or an exclusive NOR function, then the PSK of the bit stream at Tx Signal In can be present at Tx Signal Out.

FIG. 5illustrates a method500for transmitting a signal from an existing power line to a host device, in accordance with an embodiment of the present invention. At502, a signal received from a power line is demodulated into a sine signal and a cosine signal. At504, direct current values of the sine and cosine signals are determined. At506, the absolute values of the sine and cosine signals are determined. Based on the absolute values, the magnitude of the sine and cosine signals is determined at508. At510, based on the magnitude, a bit stream of data is created in order to transmit the data to the host device.

FIG. 6illustrates a method600for transmitting a signal received from a host device onto an existing power line, in accordance with an embodiment of the present invention. At602, a communicated bit stream and with a clock is received at the modem. At604, the communicated bit stream is transformed into a transmitted signal using the clock cycle.

The method steps performed inFIGS. 5 and 6may be performed by a computer program, encoding instructions for the nonlinear adaptive processor to perform at least the methods described inFIGS. 5 and 6, in accordance with an embodiment of the present invention. The computer program may be embodied on a computer readable medium. A computer readable medium may be, but is not limited to, a hard disk drive, a flash device, a random access memory, a tape, or any other such medium used to store data. The computer program may include encoded instructions for controlling the nonlinear adaptive processor to implement the methods described inFIGS. 5 and 6, which may also be stored on the computer readable medium.

The computer program can be implemented in hardware, software, or a hybrid implementation. The computer program can be composed of modules that are in operative communication with one another, and which are designed to pass information or instructions to display. The computer program can be configured to operate on a general purpose computer, or an application specific integrated circuit (“ASIC”).

Many distributed systems share common sensors and instruments along with a common power line supplying current to the system. A communication technique and circuit have been developed that allow for the simple inclusion of an instrument, sensor, or actuator node within any system containing a common power bus. Wherever power is available, a node can be added, which can then draw power for itself, its associated sensors and its actuators from the power bus all while communicating with other nodes on the power bus.

The technique modulates a DC power bus through capacitive coupling using OOK, and receives and demodulates the signal from the DC power bus through the same capacitive coupling. The circuit acts as serial modem for the physical power line communication. The circuit and technique can be made of commercially available components or be included in an ASIC design that allows for the circuit to be included in current designs with additional circuitry or embedded into new designs.

This device and technique moves computational, sensing, and actuation abilities closer to the source, and allows for the networking of multiple similar nodes to each other and to a central processor. This technique also allows for reconfigurable systems by adding or removing nodes at any time. The technique can do so using nothing more than the in situ power wiring of the system.