Abstract:
There is provided an arrangement of components for use in a power line communication system. The arrangement includes a modem for providing an output to a power line, a sensor for sensing a parameter of the output; and a controller for adjusting a power of the output based on a value of the parameter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application is claiming priority of U.S. Provisional Patent Application Serial No. 60/424,064, filed on Nov. 6, 2002, the content of which is herein incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to power line communications (PLC), and more particularly, to a configuration of a modem having an optimized output power level over its operating frequency spectrum.  
           [0004]    2. Description of the Related Art  
           [0005]    In a power line communication (PLC) system, output power of a transmitter in a wideband power line modem is coupled to a power line. The power line has an impedance magnitude characteristic and a phase characteristic that vary widely across a frequency band of the transmitter. The transmitter can be modeled as a Thevenin equivalent circuit having a fixed voltage source and a mainly resistive source impedance. As a result of an impedance mismatch between source and load, signal power coupled to the power line varies widely over the transmitter frequency band.  
           [0006]    When the signal power level is limited to a highest level compliant with regulatory limits, the limit is set for a frequency where power coupling and power line radiation efficiency are most efficient. This frequency is referred to herein as f max-rad .  
           [0007]    [0007]FIG. 1 is a block diagram of a prior art modem arrangement with a flat transmitter spectrum. A modem  100  is attached to a power line  120  via a signal coupler  125 . A functional internal structure of modem  100  is represented by a modem transmitter signal generator  105 , a power control system  110 , and a power amplifier  115 . Signal generator  105  and power control system  110  may be physically embodied in the same module of hardware and software, but are illustrated here separately for clarity.  
           [0008]    Graph  150  shows a simplified variation of electromagnetic radiation intensity for modem  100 . Modem power  155  is constant across a frequency band and is limited to P max1    160  to prevent radiation intensity  162  from exceeding radiation limit  165  at frequency f max-rad    170 . However, at other frequencies, the coupled power will be lower than that allowed by regulatory limits, and thus, performance of modem  100  is less than optimal.  
         SUMMARY OF THE INVENTION  
         [0009]    An embodiment of the present invention is an arrangement of components for use in a power line communication system. The arrangement includes a modem for providing an output to a power line, a sensor for sensing a parameter of the output, and a controller for adjusting a power of the output based on a value of the parameter.  
           [0010]    Another embodiment of the present invention is a method employed in a power line communication system. The method includes providing an output from a modem to a power line, sensing a parameter of the output, and adjusting a power of the output based on a value of the parameter.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a block diagram of a prior art modem arrangement with a flat transmitter spectrum.  
         [0012]    [0012]FIG. 2 is a block diagram of a modem arrangement using a sensor to feed back information to a power control system, in accordance with the present invention.  
         [0013]    [0013]FIG. 3 is a block diagram of a modem arrangement using modem transmitter spectral control based on sensing electromagnetic radiation.  
         [0014]    [0014]FIG. 4 is a block diagram of a modem arrangement using modem transmitter spectral control based on sensing signal voltage on a power line.  
         [0015]    [0015]FIG. 5 is a block diagram of a modem arrangement using modem transmitter spectral control based on sensing signal current on a power line.  
         [0016]    [0016]FIG. 6 is a block diagram of a modem arrangement using modem transmitter spectral control based on sensing real power out of a modem transmitter. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0017]    Many wideband modems have a mechanism, termed a power mask, to set a separate signal power level for each of several frequency sub-bands. The power mask is often realized as part of a digital processing operation involved in generating a signal from the modem. In an embodiment of the present invention, the power mask is used to reduce the power at f max-rad  and raise the power at other frequencies. This improves communications performance while ensuring compliance to radiation limits.  
         [0018]    Ideally, an electromagnetic field sensor is used as an input to an automatic mechanism for optimizing the power mask. Alternatively, a voltage or current sensor may be used to sense the power level on the power line. While this technique of optimizing the power mask to compensate for variations in sensed signal voltage or current ignores radiation efficiency variation of the power line over frequency, a system operator can perform radiation measurements and determine a maximum power level that is compliant with radiation limits.  
         [0019]    For medium or high voltage lines, voltage or current sensors may be very expensive. An alternative to the use of voltage or current sensors is to build a sensor into the modem, where the sensor senses a real component of modem output power. The power mask then adjusts the real component of the output power to be as uniform as possible over the modem&#39;s transmitter frequency band.  
         [0020]    A further improvement measures or calculates coupling efficiency of the power line coupler, when the coupler is connected to a power line, and compensates for a variation of coupling efficiency over the frequency band. The coupling efficiency may be expressed as a ratio of power coupled to the power line divided by the real component of the modem&#39;s output power.  
         [0021]    [0021]FIG. 2 is a block diagram of a modem arrangement using a sensor to feed back information to a power control system, in accordance with the present invention. The arrangement in FIG. 2 includes a modem  200  and a sensor  215 .  
         [0022]    Modem  200  provides an output to power line  120  via coupler  125 . Modem  200  includes a modem transmitter signal generator  105 , a power amplifier  115  and a power control system  210 .  
         [0023]    Sensor  215  detects electromagnetic radiation intensity output by modem  200  and outputs a signal that is proportional to the electromagnetic radiation intensity. The signal is provided from sensor  215  to power control system  210  to modify a signal spectrum from modem  200  in order to provide an optimized spectrum. The optimized spectrum provides maximum output power from modem  200  to power line  120  consistent with avoidance of non-compliance with maximum allowed electromagnetic radiation intensity. Thus, power control system  210  maximizes modem power  255  while limiting modem power  255  to a predetermined level of electromagnetic radiation.  
         [0024]    Assume that the output of modem  200  includes a first frequency sub-band and a second frequency sub-band. Modem  200  sequentially transmits over the first frequency sub-band and the second frequency sub-band, and power control system  210  adjusts the power for the first frequency sub-band and the power for the second frequency sub-band.  
         [0025]    Graph  250  shows modem power  255 , increased from level P max1 ,  160  to a maximum level P max2    260  modified by a power mask  255 . Modem power  255  has reduced power levels over a most radiative frequency span  275  so as to not exceed radiation limit  165 .  
         [0026]    [0026]FIG. 3 is a block diagram of a modem arrangement using modem transmitter spectral control based on sensing electromagnetic radiation. A modem  300  provides an output to a power line  320 . A sensor  315  senses radiation field strength of the output of modem  300  via an antenna  325 . An output of sensor  315 , which is proportional to the radiation field strength, is fed back to a power control system  310  in modem  300 .  
         [0027]    [0027]FIG. 4 is a block diagram of a modem arrangement using modem transmitter spectral control based on sensing signal voltage on a power line. A modem  400  provides an output to a power line  420 . A voltage sensor  415  senses a voltage level of the output of modem  400  on power line  420  via a wire  425 . An output of sensor  415 , which is proportional to the voltage level, is fed back to a power control system  410  in modem  400 .  
         [0028]    [0028]FIG. 5 is a block diagram of a modem arrangement using modem transmitter spectral control based on sensing signal current on a power line. A modem  500  provides an output to a power line  520 . A signal current sensor  515  senses a signal current level of the output of modem  500  on power line  520  via sensing transducer  525  and a cable  530 . An output of sensor  515 , which is proportional to the signal current level, is fed back to a power control system  510  in modem  500 .  
         [0029]    [0029]FIG. 6 is a block diagram of a modem arrangement using modem transmitter spectral control based on sensing real power out of a modem transmitter. FIG. 6 illustrates a system that can be built entirely within a modem. A modem  600  provides an output to a power line  620 . A phase detector  615  senses voltage through a connection  645  and senses current through a current-voltage transducer  660  and a cable  665 . An output  650  of phase detector  615 , which is proportional to the product of the voltage and the component of current that is in phase with the voltage, which is proportional to the real power supplied by the modem, is fed back to a power control system  610  in modem  600 .  
         [0030]    [0030]FIG. 6 also illustrates an additional optional improvement. A power meter  670  detects and indicates a power level of the electromagnetic field radiated by power line  620  and originating from a signal from modem  600 , at a location near power line  620  via an antenna  675 . Modem  600  includes a modem signal generator  605  that is programmable to sweep through transmitter sub-bands. An installing technician or automated system calculates a radiation efficiency curve for each sub-band. The curve is calculated as a ratio of (a) field strength of the electromagnetic field as indicated by power meter  670 , and (b) power as indicated at output  650 . The inverse of the curve is programmed by the installing technician or automated system into the power control system  610  to compensate for factors outside of a control loop of modem  600 . This control loop includes modem  600 , phase detector  615  and connection  645  and current-voltage transducer  660 . Power control system  610  adjusts power out of modem  600  to compensate for variations in the ratio over a transmitter frequency band of modem  600 . Such factors vary over the frequency band and include power line signal coupler efficiency and power line radiation efficiency.  
         [0031]    It should be understood that various alternatives and modifications of the present invention could be devised by those skilled in the art. Nevertheless, the present invention is intended to embrace all such alternatives, modifications and variances that fall within the scope of the appended claims.