Patent Publication Number: US-2010111199-A1

Title: Device and Method for Communicating over Power Lines

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to systems, devices and methods for communicating over power lines, and more particularly to systems, devices and methods for communicating over power lines using multiple communication channels. 
     BACKGROUND OF THE INVENTION 
     The power system infrastructure includes power lines, transformers and other devices for power generation, power transmission, and power delivery. A power source generates power, which is transmitted along high voltage (HV) power lines for long distances. In the U.S., typical voltages found on HV transmission lines range from 69 kilovolts (kV) to in excess of 800 kV. The power is stepped down to medium voltage (MV) power at regional substation transformers. MV power lines often carry power through neighborhoods and populated areas, and may comprise overhead power lines or underground power lines. Typical voltages found on MV power lines power range from about 1000 V to about 100 kV. The power is stepped down further to low voltage (LV) levels at distribution transformers. LV power lines typically carry power having voltages ranging from about 100 V to about 600 V to customer premises. 
     A power line communication system uses portions of the power grid (i.e., the power system infrastructure), such as the MV and LV power lines, to carry communications between various locations. For example, power utility companies may read power usage data from the utility meters located at consumer premises. Such data may be received from an automated meter by a power line communication device and transmitted over other power lines to a utility data center. Another example is broadband over power line internet access in which a power line communication system is adapted to deliver broadband internet access to subscribers. For example, a power line communication system may be coupled to the Internet at a point of presence (POP) and carry broadband communications between the POP and subscriber locations using power lines and other media such as fiber. At a subscriber location (residence or business), computing devices may be coupled to the power line communication system (PLCS) using a power line modem directly or indirectly. Such a power line communication may also provide video and VoIP services. 
     As the use of PLCS&#39; expands, there is a need to deliver communications in an increasingly efficient and flexible manner. Further, as the amount of services delivered over the power lines grows, there is an increasing need to be able to reliably and effectively use the power lines for other communications, such as for “reading” automated meters, for controlling and maintaining the utility infrastructure, for maintaining the power line communication systems itself, and for various other uses. These and other needs may be addressed by one or more embodiments of the present invention. 
     SUMMARY OF THE INVENTION 
     The present invention provides a device and method for communicating over a power line. In one embodiment, the device includes a multiband media access control (MAC) layer configured to select one of a plurality of frequency bands for communication and a multiband physical layer configured to communicate directly with said multiband MAC layer and to communicate over the power line via any one of the plurality of frequency bands. The multiband MAC layer may include a power control module configured to provide information to said physical layer to control the transmission power of data transmitted by said physical layer and a modulation control module configured to select one of plurality of modulation schemes for data transmitted by said physical layer. The physical layer may include a plurality of physical drivers with each physical driver configured to transmit and/or receive data in a different one of the plurality of frequency bands. 
     The invention will be better understood by reference to the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is further described in the detailed description that follows, by reference to the noted drawings by way of non-limiting illustrative embodiments of the invention, in which like reference numerals represent similar parts throughout the drawings. As should be understood, however, the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
         FIG. 1  is a diagram of a conventional OFDM protocol stack; 
         FIG. 2  is a diagram of a multiband protocol stack, in accordance with an example embodiment of the present invention; 
         FIG. 3  is a block diagram of a multiband MAC layer and multiband physical layer of a multiband protocol stack in accordance with an example embodiment of the present invention; 
         FIG. 4  is a block diagram of a communication device which couples to a power line network, in accordance with an example embodiment of the present invention; 
         FIG. 5  is a functional block diagram of power line communication device supporting broadband power line communications and multiband power line communications, in accordance with an example embodiment of the present invention; 
         FIG. 6  is a functional block diagram of power line communication device supporting multiband power line communications and wireless network communications in accordance with an example embodiment of the present invention; 
         FIG. 7  is a functional block diagram of power line communication device having multiple interfaces, in accordance with an example embodiment of the present invention; 
         FIG. 8  is a block diagram of a power line communication system, according to an example embodiment of the present invention; 
         FIG. 9  is a flow chart of a method for transmitting communications using a multiband protocol stack according to an example embodiment of the present invention; and 
         FIG. 10  is a flow chart of a method for receiving communications using a multiband protocol stack according to an example embodiment of the present invention. 
         FIG. 11  is a flow chart of a method for communicating data using a multiband protocol stack according to an example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular networks, communication systems, computers, terminals, devices, components, techniques, data and network protocols, power line communication systems (PLCSs), software products and systems, enterprise applications, operating systems, development interfaces, hardware, etc. in order to provide a thorough understanding of the present invention. 
     However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. Detailed descriptions of well-known networks, communication systems, computers, terminals, devices, PLCSs, components, techniques, data and network protocols, software products and systems, operating systems, development interfaces, and hardware are omitted so as not to obscure the description of the present invention. 
     According to an embodiment of the present invention, a power line communication system implements multiband power line communications, that may operate in a larger (multiband) frequency band divided into multiple frequency bands (with each band being used to carry multiple carrier frequencies). In a specific embodiment, there may be multiple frequency bands within the range of 50 kHz and 500 kHz. Thus, the multiband system may be sometimes use narrow bands. Each band may be a fixed width band, such as, for example, multiple 50 kHz bands. In each band (e.g., each 50 kHz band), the communication devices of the system may employ a fixed number of equally spaced carrier frequencies or a different and/or variable number of carriers. The specific frequency range and the specific allocation of carrier frequencies and frequency bands may vary in differing embodiments. A frequency band selected for use from among the multiple bands is referred to herein as a band or channel. In some embodiments, the multiple bands may be contiguous (except for guard bands and/or notches) and in other embodiments, the various bands may be spaced apart and separated by bands used for other communication devices. 
     In some embodiments of the present invention, power line communications may be sent and received via low voltage power lines and/or medium voltage power lines using a power line communication device (PLCD). In various embodiments the power lines may be overhead power lines and/or underground power lines. A given PLCD may use one or more bands to communicate with other devices. Such sub-bands need not be adjacent frequency bands. For a given communication, a specific channel (i.e., a band) within the spectrum of the larger multiband frequency band may be used. Select bands may be enabled or disabled dynamically during normal operation, typically without adversely impacting performance. For example, a specific PLCD may determine that signal-to-noise ratios are low for first band and switch to another band for communications with select remote devices or all devices. 
     One advantage of the multiple band power line communication system is that high data rates may be achieved. For example, in a system for communicating with hundreds of residential power meters each band may provide an approximate data-rate of 128 Kbps over a 50 KHz band. Such a system maybe extended with present invention for multiple operational bands (e.g., from 50 KHz to 500 KHz i.e. nine bands) to provide a combined data-rate of greater than 1 Mbps. 
       FIG. 1  shows various layers in a conventional (prior art) OFDM communication protocol stack  100 . The stack  100  includes a physical layer  102 , which maybe partly or completely implemented in hardware. A given physical layer is typically designed to communicate via a single predetermined frequency band. 
     A media access control (MAC) layer  104  provides channel access control and includes an associate MAC address, making it possible to deliver data packets to a destination within the network. The channel access control mechanisms provided by the MAC layer  104  make it possible for several devices connected to the same physical medium (e.g., power line) to share the medium. In addition, time synchronization (if necessary) may be achieved with a network&#39;s central controller device via the MAC layer  104 . The MAC layer  104  also acts as an interface between a convergence layer  106  (e.g., Internet Protocol layer) and the physical layer  102 . The convergence layer  106  provides logical address mapping for the specific communication device so that software running at the application layer  108  may access data being received, and output the data being sent. 
       FIG. 2  shows various layers in a multiband protocol stack  120 , according to an example embodiment of the present invention, such an embodiment implemented by a modem suitable for communicating in a power line communication system that employs multiband communications. The multiband protocol stack  120  includes an application layer  108 , convergence layer  106 , and MAC layer  104 , similar to those of the OFDM stack  100  discussed above. However, the multiband protocol stack  120  also includes a multiband MAC layer  122 . Further, the multiband protocol stack  120  includes a multiband physical layer  124 , rather than a single band physical layer  102 . The multiband physical layer  124  enables communications using a plurality of different frequency bands within an overall operational frequency spectrum, (e.g., 50 kHz to 500 kHz). 
     As discussed, the term “band” (and channel) in the context of the multiband protocol stack  120  of one embodiment refers to a plurality of OFDM (frequency) carriers that collectively communicate data from a first device (the modulating device) to a second device (the demodulating device). Typically, the carriers of a band are contiguous (i.e., grouped together) although in some instances certain smaller groups of frequencies within a band may be notched out (filtered out) so as not to interfere with other devices known to user the notched frequencies. 
     A prior art single band system, such as one implementing OFDM protocol stack  100 , typically uses only one set of OFDM carriers. However, a multiband system having M bands uses M sets of OFDM carriers—typically with each set of carriers being mutually exclusive of other OFDM carriers. For example, a two band system may use two sets of mutually exclusive OFDM carriers. In the multiband system each set of OFDM carriers (i.e., each band) may or may not comprise an equal number of carriers, and therefore, various bands may have different bandwidths (e.g., 40 KHz for one, 50 KHz for a second, and 60 KHz for a third). Thus, some bands may have greater communications capacities than other bands. 
     In one embodiment, at any given time a PLCD may operate at any band among the multiple bands. The multiband MAC layer  122  selects the physical channel (corresponding to a band) so that the MAC layer  104  operates seamlessly, similar to as if it were in a single band OFDM modem. Accordingly, the application layer  108 , convergence layer  106  and MAC layer  104  may be implemented seamlessly. For outgoing communications, the upper MAC layer  104  passes a data packet to the multiband MAC layer  122 , which categories the data packet for transmission by one of the physical layers  124 . 
       FIG. 3  shows a detailed view of the multiband MAC layer  122  and multiband physical layer  124  according to one embodiment of the present invention. The multiband MAC layer  122  includes a data multiplexer/demultiplexer  132 , a band controller  134 , and channel access extensions module  136 . When transmitting data, the MAC layer  104  passes data to the multiband MAC layer  122 . The data multiplexer/demultiplexer  132  of the multiband MAC layer  122  categories each block of data for transmission by one of the physical band drivers  144 . The band to be used for transmission (which determines the physical driver  144  to be provided the data for transmission) may be determined from the size of data block, the capacity of a given band based on channel conditions, a channel access policy for a given band, and/or other information. For data being received, the data multiplexer/demultiplexer  132  removes band specific information from the received data packet and passes the data as a MAC data packet to the MAC layer  104 . 
     The band controller  134  may include a power control module  138 , a modulation control module  140 , and a forward error correction (FEC) module  142 . The band controller  134  keeps track of physical channel conditions (e.g., stores data of channel noise and attenuation) on each operational band. For example, the channel noise and attenuation may be different at different frequencies (thus on different bands). The conditions may be monitored on each band through queries to corresponding physical layer driver. Channel noise may vary over time, thus making it important in some embodiments to regularly monitor noise. Thus, the physical drivers  144  may provide direct or indirect (where the actual values maybe derived from other available statistics) noise and attenuation values (and/or data other physical conditions) to the band controller  134 . The band controller  134  may periodically (and/or continuously) store values of physical conditions in order to obtain a larger perspective over time for the conditions of each band. 
     The band controller  134  interfaces with each available physical layer driver  144   a - m  (corresponding to each band) and also may receive operational parameters such as, for example, Receive Signal Strength Indicator (RSSI), Signal-to-Noise Ratio (SNR), CRC (Cyclic Redundancy Check) failure count, and/or other parameters. Based on these conditions (e.g., channel noise and attenuation for each band) and operational parameters, the band controller  134  (e.g., one of its respective sub-blocks Power Control  138 , Modulation Control  140  and/or FEC control  142 ) may also define one or more transmission and/or reception parameters for each band. The parameters that maybe defined, besides the band to be used for communication, may include, for example: transmission power, modulation scheme, forward error correction, pre-emphasis, post emphasis, and/or the (FEC) scheme. For example, if channel conditions deteriorate, the band controller  134  may dynamically determine to increase the transmission power, to a use a robust modulation scheme, to use a different band for communications, or to FEC code rate one half or some combination of all. For reception, an additional parameter that may be defined includes the amplification of input signals (e.g., Automatic Gain Control or (AGC)). In some embodiments, operational parameters and/or channel conditions also may be used (e.g., with other factors) to select the band, modulation scheme, error correction, and/or power transmission, etc., for initial communications with a remote device. 
     The channel conditions and operational parameters may be maintained separately for each remote PLCD with which a given PLCD communicates. For example, the power control module  138  may maintain and update a matrix of optimal transmission power and automatic gain control (for reception) settings for each peer (remote) power line communication device across each band. In other embodiments, additional and/or other settings may be stored. 
     For example, a first embodiment may use open loop power control to set the transmission power to be used when transmitting data to each remote PLCD in each band. Using the RSSI and SNR values of received data from each remote PLCD, the power control module  138  estimates the channel attenuation and noise to make an autonomous determination of the transmission power (e.g., which may result in an increase and/or decrease of the transmission power over time as the RSSI and SNR values change) to be used. 
     In another embodiment, a closed loop power control process may be used to set the transmission power to be used when transmitting data to each remote PLCD in each band. In this embodiment, the remote device transmits a reference signal with a fixed (known) transmission power (e.g., at the request of the PLCD setting the transmission power). The physical layer(s)  144  receiving the reference signal (which may be simultaneously received in a single band, select bands, or in all bands) will then provide feedback on the RSSI of the received signal (and/or other data) which may be used by the power control module  138  to adjust the transmission power to provide the desired quality of communications. The reference signals may be sent periodically (e.g., every second, minute, hour, etc.) from each PLCD in order to continue to adjust the transmission power to be used by each PLCD. 
     The modulation control module  140  maintains and updates a matrix of modulation schemes to be used for communication with each PLCD (or other per device) in each band. The FEC control module  142 , depending on certain parameters (signal to noise ratio (SNR), retransmissions, cyclic redundancy check (CRC) failure count, and/or other data), defines error correction schemes to be used for communication with each device in each band. 
     The channel access extensions module  136  includes logic for band specific channel access mechanisms (e.g., logic for determining the band to use for a communication). More specifically, the channel access extensions module  136  receives operational input data from band controller module  134  and applies band specific channel access algorithms to ensure conformance to regulations pertinent to that channel. In one embodiment each frequency band may be controlled independently of the other bands, although the rules used for selecting a channel may be the same. For example, there may be channel access rules which use start of contention period, time of beacon transmission, and/or other information to select a band. Further, if one PLCD uses a first band at a given moment in time to send a communication, another device may use another band at the same time to send a communication (e.g., sent to different devices or the same device). In another embodiment each frequency band is not independently controlled. Instead, the entire operational frequency spectrum, comprising multiple bands may be used by only one device in the system at a given instant of time and that device may transmit using a single band, multiple bands, or all bands concurrently to one or more (or all) devices. This option allows for low cost implementation while compromising on performance. 
     The multiband physical layer  124  may include a transceiver circuitry coupled to a network medium for transmitting and receiving communications. In some embodiments, the physical layer  124  may enable multiple PHY drivers (including their transceivers)  144   a - m  to concurrently transmit and receive data in multiple bands (providing increased aggregate data-rates). In other embodiments only one PHY driver may be enabled at a given point of time, such may not result in enhanced data-rate, but instead provide an advantage of low cost and frequency agility. In some embodiments in which one of many available PHY drivers are used, the stack may allow for dynamic, real-time switching from one active PHY driver to other, thus enabling change of band in real-time, while others may allow only non-real-time switching between PHY drivers. Thus, in some embodiments each physical driver  144  may be designed to communicate (transmit and receive) using a predetermined frequency band (corresponding to one of the M bands). 
     The digital portions of the multiband physical layer  124  may be implemented in hardware and/or software. In some embodiments, a hardware implementation of the digital portions may comprise a dedicated ASIC while in other embodiments, it may be implemented via use of a Field Programmable Gate Array (FPGA). A software implementation typically may include implementation on a digital signal processor (DSP). Thus, the layer  124  may include (or be implemented with) a processor. The analog portions (e.g., the physical layers) of the multiband physical layer  124  may be implemented using an Analog-to-digital (A/D) converter and associated circuitry to comprise an analog front end (AFE) 
     Because different bands may have different bandwidths and different modulation schemes may be used in each band, the number of carriers in each band and thus the data transferred per band and per symbol and in each band may be different. The channel access extensions module  136  in the multi-band MAC layer  122  factors in such band specific issues and provides input to the data multiplexer/demultiplexer  132  which may segment, aggregate and or not perform any action on data; thus making it suitable for communication on any specific band. 
     Power Line Communication Device Embodiments 
       FIG. 4  shows a power line communication device (PLCD)  200 , according to an example embodiment of the present invention. The PLCD  200  includes a pair of interfaces, including a power line interface  202  and another network interface  204 . The power line interface  202  couples to a power line, such as a medium voltage power line or a low voltage power line, allowing communications to be sent and received using power lines. The other network interface  204  may couple the PLCD  200  to another portion of the power line network or to a non-power line network, such as a wireless network. Different portions of the power line network may implement different protocols and/or different communication schemes, which may be bridged by this example embodiment. For example, in one embodiment, the power line interface  202  may couple to a portion of a power line network implementing the multiband PLC communication scheme, as shown in  FIG. 5   a,  while in others a narrowband scheme may be used as described with respect to  FIG. 5   b  in which case power line interface  202  may employ a conventional OFDM protocol stack  100 . The other network interface  204  may couple to a portion of the power line network implementing a broadband PLC communication scheme (e.g., a wideband communications scheme or one operating in a frequency spectrum that is at least as broad as two, three, four or more multibands or narrow bands—e.g., operating in frequencies from 1 MHz to 80 MHz). 
     A controller  206  provides control and routing functions (e.g., bridging, routing, and/or switching) for the interfaces  202 ,  204 . Thus, the controller  206  may have an address table stored in memory for determining the correct address to insert into a data packet for transmission (e.g., insert a MAC address based on the IP address of the data packet). Note that while the controller  206  is shown between the interfaces  202  and  204 , in practice, in some embodiments the controller  206  may simply share a bus with the two interfaces while in others the controller may reside on either of interface  202  or  204  (and be integrated with such interface). Accordingly, a given communication may be received from a power line via the power line interface  202 , and then directed to the network interface  204  where it may be packaged for transmission onto another portion of the power line network or onto a non-power line network, such as a wireless network. Similarly, a communication may be received from a network at the network interface  204 , and then directed to the power line interface  202  where it may be packaged for transmission onto a power line network. 
     The power line interface  202  may include a coupler  210  which couples a modem  212  to one or more power line conductors so that signals may be transmitted and received via power lines. The power line interface  202  may also include an analog front end comprising appropriate filter circuitry, amplifier circuitry, surge suppressant circuitry, and other such circuitry (not shown). The power line interface  202  may also include the multiband protocol stack  120 , which may be implemented in both hardware and software such as, for example, as described herein. However, the power line interface  202  also may be implemented via a plurality of conventional (e.g., OFDM) modems (e.g., modem chip sets), with each modem configured to communicate via separate band. Note that although the modem  212  is shown as a separate box in the figure, the modem  212  may formed, in part, by the multiband protocol stack  120 . 
     The network interface  204  may be formed by another power line interface substantially the same as interface  202 , by a broadband power line interface, or by an alternative network interface such as for communicating over a coaxial cable, twisted pair, fiber optic conductor, or wirelessly. The network interface  202  also may (optionally) include a coupler  220  which couples a modem  222  to a network medium (such as a power line). Alternately, the modem  222  may comprise a transceiver and include an antenna that allows the modem  222  to communicate wirelessly. The network interface also may have a protocol stack  224 , such as the multiband protocol stack  120  or a broadband PLC protocol stack or other stack suitable for the communications desired. As discussed, the protocol stack  224  may be implemented as part of the modem  222 . 
     The controller  206  controls the operation of the PLCD  200 , and may include a processor and memory storing program code that controls the operation of the processor. In an example embodiment the controller  206  matches data with specific messages (e.g., control messages) and matches the addresses of data packets with destinations (i.e., perform routing, bridging, and/or switching), performs traffic control functions, performs usage tracking functions, authorizing functions, throughput control functions and other services. The processor may also be programmed to receive software and commands (received via either interface) and to process the commands and store the received software in memory for execution. 
       FIG. 5   a  depicts the functional components of an example power line communication device  200   a  which communicates via a broadband power line communication network  302  and a multiband power line communication network  304 . The PLCD  200   a  includes components similar to those of PLCD  200  of  FIG. 4 , except that the network interface is illustrated as a broadband power line interface. Thus, a first network interface includes a broadband power line communication (BPL, such as one implemented in frequencies in the range of 1 MHz to 80 MHz) modem  306  that may use OFDM scheme, wavelet or any other equivalent communication scheme (and/or may include a conventional protocol stack  100 ). The second network interface includes a multiband powerline modem (e.g., for power line communications implemented in frequencies of the KHz range). Some embodiments of the PLC interface may be implemented using multiple modems, each having a conventional protocol stack  100  (with an analog front end that is configured to communicate via any one of a plurality of frequency bands), while other embodiments may be implemented using multiband protocol stack  124  and operates as described above. The controller  310  may include a memory storing program code and a processor perform routing functions, interworking functions, and buffering as described above. In an example implementation, the broadband modem  306  communications may traverse medium voltage power lines. For some communications, the controller  310  may cause the broadband modem  306  to re-transmit the data back onto the medium voltage power lines through the first interface (i.e., to repeat data). For other data, the data may directed to the multiband modem  306  which transmits the communication toward a remote device over a low voltage power line using one of the bands. For example, a communication (data packet) traversing a broadband power line communication network  302  may have a destination address for a device served by the PLCD  200   a.  When the PLCD  200   a  receives the communication and reads the destination address (e.g., IP address or any protocol address such as one that identifies the destination endpoint), the controller may re-address the data packet (if necessary) and direct the data onto a low voltage power line via the multiband modem  308  at a selected band. Such a device may be suitable for routing data around distribution transformers between the MV and LV power lines. The power line network interface having the multiband modem  308  in this example operates as described above with regard to  FIG. 4 , and in similar manner as described above for the multiband protocol stack described with regard to  FIGS. 2-4 . 
     For communications originating from a device on the multiband network  304  (e.g., a low voltage power line), the multiband modem  308  processes the received communication and may provide the data to the controller  310  (or, in some instances directly to the broadband modem  306 ). The controller  310  may then direct the data packet to the broadband modem  306  for communication onto the broadband PLC network  302 . 
     The power line modem  308  may operate at one given time at a specific band of the multiple frequency bands. For example, referring to  FIGS. 4 and 5   a  the modem  212 / 308  may operate in a fixed width of 50 kHz band, occurring anywhere within a supported spectrum of 50 kHz to 500 kHz. In another embodiment, the modem  308  may concurrently operate (e.g., transmit or receive) in all of the bands within the larger frequency range (e.g., 50 KHz to 500 KHz). The specific bands and specific carrier frequencies may vary depending on the embodiment and implementation thereof. Further, the channel access extensions module  136  in the multiband MAC layer  122  (see  FIG. 3 ), adapts automatically to respect any regulatory channel access procedures that may apply for an operational frequency band. For example, when configured for operations in CENELEC Band C in Europe, the system may follow channel access requirement rules specified for this band. 
     The broadband modem may communicate via broadband frequencies from 1 MHz to 80 MHz. Thus, from a functional perspective, the PLCD  200   a  provides a seamless interworking bridge between narrowband and broadband network. 
       FIG. 5   b  illustrates an example embodiment which communicates via a broadband power line communication network  302  and a narrowband power line communication network  304  (which need not be a multiband power line network). The PLCD  200   a  includes the components similar to those of PLCD  200   a  of  FIG. 5   a,  except that modem  308  comprises a narrowband modem  308  (and need not be a multiband modem). Thus, the first network interface includes a broadband power line communication (BPL, such as one implemented in 1 to 80 MHz range) modem  306  that includes a conventional protocol stack  100  and is configured to communicate via broadband communications. As discussed, as used herein broadband communications refers to communications that communicate data signals in a frequency band that is greater than one MHz in width, more preferably greater than greater than 5 MHz in width, still more preferably greater than 10 MHz in width, and even more preferably greater than 20 MHz in width. As discussed, in some embodiments the operational frequency may anywhere from about 1 MHz to about 80 MHz. The second network interface includes a narrowband powerline modem  308  (e.g., for power line communications implemented in frequencies of the KHz range). As used herein narrowband communications refers to communications that communicate data signals in a frequency band that is less than 500 KHz in width, more preferably less than 200 KHz in width, still more preferably less than 100 KHz in width, and still more preferably less than 55 KHz in width. In this embodiment, the narrowband power line modem  308  may include a PLC interface that uses a conventional protocol stack  100 . The controller  310  may include a memory storing program code and a processor perform routing functions, interworking functions, and buffering as described above. In an example implementation, the broadband modem  306  communications may traverse medium voltage power lines. For some communications, the controller  310  may cause the broadband modem  306  to re-transmit the data back onto the medium voltage power lines through the first interface (i.e., to repeat data). For other data, the data may directed to the narrowband modem  308  which transmits the communication toward a remote device over a low voltage power line using a narrowband communication. For example, a communication (a data packet) traversing a broadband power line communication network  302  may have a destination address for a device served by the PLCD  200   a.  When the PLCD  200   a  receives the communication and reads the destination address (IP or other protocol address), the controller may re-address the data packet (if necessary) and direct the data onto a low voltage power line via the narrowband modem  308 . Such a device may be suitable for routing data around distribution transformers between the MV and LV power lines. 
     For communications originating from a device on the narrowband network  304  (e.g., a low voltage power line), the narrowband modem  308  processes the received communication and provides the data to the controller  310 . The controller  310  may then direct the data packet to the broadband modem  306  for communication onto the broadband PLC network  302 . 
     As discussed, the narrowband power line modem  308  of  FIG. 5   b  may communicate using a single narrow frequency band. In other embodiments, the narrowband power line modem  308  may use multiple (different) narrow frequency bands for concurrent (or non-concurrent) communications. Such an embodiment may use a one or more modem chip sets (and/or one or more associated analog front ends) that includes a conventional protocol stack  100 . For example, in a first embodiment the modem  308  may operate in a fixed width of 50 kHz band, occurring anywhere within a supported spectrum of 50 kHz to 500 kHz. The specific band and specific carrier frequencies may vary. In a second embodiment, the narrowband modem  308  may operate in two different bands having fixed widths of 50 kHz, occurring anywhere within a supported spectrum of 50 kHz to 500 kHz. 
     As discussed, the broadband modem may communicate via broadband frequencies from 1 MHz to 80 MHz. Thus, from a functional perspective, the PLCD  200   a  provides a seamless interworking bridge between narrowband and broadband network. 
     In this and the other embodiments described herein, when the device is communicating over a low voltage power line, the data signals may be differentially transmitted (and received) over the first and second energized power line conductors of the low voltage power line (via appropriate filtering and amplification circuitry). 
       FIG. 6  shows functional portions of another power line communication device  200   b  which communicate over a wireless network  312  and a multiband power line communication network  304 . The PLCD  200   b  includes components substantially similar to those of PLCD  200  of  FIG. 4 . A first network interface may include a wireless modem  314  (e.g., a wireless transceiver substantially compliant or compatible with one or more of IEEE 802.11 a/b/g/n, IEEE 802.15, a General Packet Radio Service (GPRS), CDMA2000 or any other prevalent standard). A second network interface includes the multiband modem  308  that includes a multiband protocol stack  120 . A controller may include the routing and interworking function module  310   a.  In an example implementation, wireless network communications may be received at the first interface and be processed by the wireless modem  314 . The controller  310  may providing routing functions and interworking functions, and may provide the data to the multiband modem  308  which transmits the data over the multiband power line communication system network  304 , such as via a medium voltage or low voltage power line. The data may addressed in a data packet (e.g., by the controller  310 ) with an address corresponding to the target destination device. The power line network interface having the multiband modem  308  operates as described above with regard to  FIG. 4 , and in similar manner as described above for the multiband protocol stack described with regard to  FIGS. 2-4 . 
     For communications originating from a device connected to the power line network  304 , the multiband modem  308  receives and processes communication and provides the data to the controller  310 . The controller  310  may, if necessary, re-address the data packet and provide the data to the wireless modem  314  for wireless transmission by the wireless modem  314 . Instead of a multiband modem  308 , other embodiments may include a narrowband modem  308  as described above. 
       FIG. 7  is a schematic showing functional portions of yet another power line communication device  200   c  which communicates over various networks, such as a broadband PLC network  302 , wireless networks  312   a,b  and a multiband PLC network  304 . The PLCD  200   c  includes functional components similar to those of the PLCD  200  of  FIG. 4 , PLCD  200   a  of  FIG. 5   a,  and PLCD  200   b  of  FIG. 6 . Note that in this schematic the protocol stacks are illustrated (instead of modems), which typically are integrated in a modem. Each interface may include a protocol stack for handling communications via its respective network. For example, a broadband PLC network interface may include a broadband (single band) PLC protocol stack  306 . One or more wireless network interfaces may include a ZigBee protocol stack  314   a  and/or a GPRS/CDMA2000 protocol stack  314   b,  or another stack that supports a wireless protocol. A multiband PLC network interface may include the multiband protocol stack  120 , according to an example embodiment of this invention. Each stack may be communicatively coupled to a controller  310   b  (that includes a processor and memory storing executable program code) that may provide routing and interworking functions. In one implementation, each protocol stack is embodied in a different integrated circuit (modem chip or chip set) and be formed of different modems. In another implementation, two or more of stacks may be formed by a single integrated circuit (modem chip or chip set) and be formed of a single modem. 
     In an example implementation, broadband power line communications may traverse medium voltage power lines and be received at PLCD  200   c,  where they are processed by the broadband PLC protocol stack  306 . The routing and interworking function module  310  of the PLCD&#39;s  200   c  controller may re-transmit the data back onto the medium voltage power lines. Alternatively, the communication may be directed to one of the other networks. For example the communication may be directed to multiband PLC protocol stack  308  (e.g., communicating via narrowband communications) which transmits the communication toward a target device over a medium voltage or low voltage power line. 
     A communication from a wireless network  312   a,b  may be processed by the corresponding wireless network protocol stack  314   a,b.  The routing and interworking function of controller  310  of the PLCD  200   c  may then transmit the data to the multiband protocol stack  308  which transmits the communication over the power line network  304 , such as via a medium voltage or low voltage power line (overhead or underground). In particular, communications received at the PLCD  200   c  destined for a destination device supported by the PLCD  200   c  (as determined by routing or bridging data stored in memory) may be directed to the multiband protocol stack  308 . Such stack  308  may package and send the data over the multiband PLC network toward the destination device using the methodology implemented by the multiband protocol stack  308 . 
     For communications originating from a device connected to the narrowband power line network  304 , the protocol stack  308  (which may either be conventional protocol stack  100  or multiband protocol stack) may process the received data signal and provide the data to the controller for routing and interworking functions, which may then provide the data to the appropriate stack for communication onto the desired network  302 ,  304 ,  312 . 
     In other embodiments the PLCD  200  may be implemented for communicating with different portions of a multiband PLC communication network  304  (such as an medium voltage power line portion and a low voltage power line portion). Such a PLCD  200   c  may include a pair of multiband PLC interfaces, each having a multiband PLC multiband protocol stack  308 . 
     Various embodiments may perform all, many, or only a few of the processes described herein. In one example embodiment, the processes illustrated in  FIG. 11  are performed. Please note, however, that these process steps may be performed in any suitable order and the invention is not limited to the sequence illustrated. In addition, some embodiments may omit some of these steps and/or include other steps. At step  702 , the data is received via a broadband communication. At  704 , the controller performs routing functions. At step  706 , one or more channel conditions are maintained and may be used (e.g., with other factor) to select a frequency band, modulation scheme, and/or transmission power. At step  708 , one or more operational parameters are maintained and may be used (e.g., with other factor) to select a frequency band, modulation scheme, and/or transmission power. At step  710 , one of the plurality of frequency bands may be selected. At step  712 , one of a plurality of modulation schemes may be selected. At step  714 , the transmission power may be determined. At step  716 , the data may be provided to the physical driver (e.g., corresponding to the selected frequency band). At step  718 , the data is transmitted by the physical driver in the selected frequency band and in a data signal modulated in accordance with the selected modulation scheme. 
     Power Line Communication System 
       FIG. 8  shows an embodiment of a power line communication system (PLCS)  400 , according to an example embodiment of the present invention. The PLCS  400  includes multiple power line communication devices  200   a  which send and receive communications using medium voltage power lines  402  and low voltage power lines  404 . In some embodiments a PLCD  200   a  may form a bypass device which receives data from a medium voltage power line  402 , and transmits the data along one or more low voltage power lines  404  thereby bypassing the power distribution transformer  406 . Similarly, data received from a low voltage power line  404  may bypass the distribution transformer  406  and be transmitted along a medium voltage power line  402  by the PLCD  200 . In some embodiments the PLCS  400  also may include a backhaul device  408  which communicates with a group of PLCDs  200   a  connected to a MV power line  402 . Thus, the backhaul device  408  may provide a path for coupling the PLCS  400  to an IP network  410  (e.g., the Internet), such as through an aggregation point  412  and point of presence (POP). 
     The PLCS  400  may implement various communication services and use various communication protocols. For example, the PLCS  400  may provide internet access via the power lines  402 ,  404  to customer premises. In an embodiment of the present invention, multiband power line communications may be used by the PLCS to communicate with various devices  420 , such as automated utility meters (e.g., power, gas, water, sewer meters), and consumer devices (e.g. faxes, computers, televisions, DVRs, VoIP telephones, etc.) and others. In yet another example, the PLCS  400  may be used only for utility communications such as meter reading (but not internet access). In another embodiment, the devices  420  may be configured to communicate utility data (e.g., power usage data, power factor data, voltage data (such as peak, RMS), current data) with one or more remote devices that may comprise automated utility meters. In one embodiment, each such device may be allocated a separate band. For example, a broadband communications protocol may be implemented for communications between a PLCD  200   a  and another PLCD  200 , or with the backhaul device  408  over the MV power line. Multiband (narrowband) communications may be implemented by each PLCD  200   a  for communications with the devices  420  coupled to the low voltage power line of that PLCD  200   a  such as utility meters and consumer devices. Such multiband communications may be implemented using the multiband protocol stack  120  as previously described. Alternately, narrowband communications may be used as discussed with respect to  FIG. 5   b.  Accordingly, a data communication may originate from a data center or other source coupled to the IP network  410 , be received into the PLCS  400  at the backhaul device  408 , then transmitted over the power lines to a PLCD  200   a  using a broadband communication protocol. The PLCD  200   a  may then repackage the data to be sent to a destination device  420  using the PLCD&#39;s multiband protocol stack  120  (or, alternately, via a conventional OFDM protocol stack  100  for narrowband communications). The destination device  420  which ultimately receives the communication may be identified by a destination address in the originally transmitted data packet. In another embodiment, the destination device  420  maybe identified by a translated destination address derived through protocol conversion by any of the intermediate interworking bridge device PLCD  200 . Similarly, a remote device  420  may send a communication to the PLCD  200   a  which receives the communication using the multiband protocol stack  120 (or, alternately, via a conventional OFDM protocol stack  100  for narrowband communications). The PLCD  200   a  repackages the communication for a broadband protocol, and then transmits the communication toward a destination (e.g., the Backhaul Device  408 ). Such destination may be at an address within the PLCS  400  or within the IP network  410 . 
     The PLCS  400  also may be coupled to a wireless network  312 . For example, a PLCD  200   b  may include a wireless network interface and a multiband PLC interface. Wireless communications may be received at the PLCD  200   b  using a wireless protocol stack  314  (see  FIG. 6 ), such as a ZigBee protocol stack  314   a  or GPRS protocol stack  314   b  (see  FIG. 7 ). Such communications may be repackaged and sent to a destination device  420  using the multiband protocol stack  120  (see  FIG. 6 ) (or, alternately, via a conventional OFDM protocol stack  100  for narrowband communications). Similarly, the device  420  may send a communication to the PLCD  200   b  which receives the communication using the multiband protocol stack  120 , which repackages the communication for a wireless protocol, and then sends the communication through the wireless network  312 . 
     As another example, a PLCD  200   c  may be coupled to both the wireless network  312  and to the power lines  402 ,  404 . Communications may originate from the IP network  410 , the wireless network  312 , or a device  420  within the PLCS  400  and be transmitted to another device  420  within the PLCS  400  or the IP network  410 . Communication paths between a given device  420  and its PLCD  200   c  may be implemented using the multiband protocol stack  120 , while communications between the PLCD  200   c  and another PLCD  200  or the backhaul device  408  may be implemented using a broadband PLC protocol stack  306 ; and communications between the PLCD  200   c  and wireless network  312  may be implemented using a wireless protocol stack  314 . 
     In some embodiments, the PLCS  400  may implement multiband communications over the entire power line network. In such embodiments, a PLCD  200  may be installed at each communication node. Each such PLCD  200  may include a pair of multiband protocol stacks  120  (each in a modem). Thus, communications between the backhaul device  408  and PLCDs  200 , among the PLCDs  200 , and to and from the devices  420  may be implemented using multiband communications. 
     Methods of Communicating Using Power lines 
       FIG. 9  depicts a process  500  for transmitting data over a power line using a PLC multiband protocol stack  120  according to an example process. At step  502 , the application layer  108  (see  FIG. 2 ) provides data to be transmitted. At step  504 , the convergence layer  106  maps the data addresses (e.g., layer 3 addressing). At step  506 , the MAC layer  104 , prepares a data packet (e.g., layer 2 addressing). At step  508 , the multiband MAC layer  122  selects the band of the multiple bands is to be used for the communication, sets power transmission, etc. and provides the data packet to the physical layer  124 . At step  510 , the physical layer driver  144  outputs the data. At step  512 , the analog front end couples the communication onto the power line  402 ,  404  (via a coupler  210  if necessary). Accordingly, the communication is transmitted using a low voltage power line  404  or medium voltage power line  402 . Error checking also may be performed. 
       FIG. 10  depicts a process  600  for receiving data via a power line using a PLC multiband protocol stack  120 . At step  602 , the communication is received via the analog front end and (in some embodiments) via the coupler  210  from a medium voltage power line  402  or low voltage power line  404 . At step  604 , the physical layer device driver  144  of the physical layer receives the data packet. At step  606  the multiband MAC layer  122  receives the data packet from the appropriate physical layer driver  144 . At step  608 , the multiband MAC layer formats the packet for the MAC layer  104 . At steps,  610 ,  612 , and  614  MAC layer processing, convergence layer processing, and application layer processing are performed to map the data and otherwise make the received data available to one or more application programs being executed by a processor included in or coupled to the PLCD  200 . 
     It is to be understood that the foregoing illustrative embodiments have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the invention. Words used herein are words of description and illustration, rather than words of limitation. In addition, the advantages and objectives described herein may not be realized by each and every embodiment practicing the present invention. Further, although the invention has been described herein with reference to particular structure, materials and/or embodiments, the invention is not intended to be limited to the particulars disclosed herein. Rather, the invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. Those skilled in the art, having the benefit of the teachings of this specification, may affect numerous modifications thereto and changes may be made without departing from the scope and spirit of the invention.