Patent Publication Number: US-2021194541-A1

Title: Long preamble and duty cycle based coexistence mechanism for power line communication (plc) networks

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS: 
     This application is a continuation of and claims priority U.S. patent application Ser. No. 16/552,911, filed on Aug. 27, 2019, which is a continuation to U.S. patent application Ser. No. 15/946,041, filed on Apr. 5, 2018 (now U.S. Pat. No. 10,396,852), which is a continuation of and claims priority to U.S. patent application Ser. No. 14/824,506, filed on Aug. 12, 2015 (now U.S. Pat. No. 9,941,929), which is a continuation of and claims priority to U.S. patent application Ser. No. 13/910,125, filed on Jun. 5, 2013 (now issued U.S. Pat. No. 9,136,908), which claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/655,558, which is titled “Long Preamble and Duty Cycle based Coexistence Mechanism for Power Line Communication PLC Networks” and was filed on Jun. 5, 2012, the disclosures of which are hereby incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     Power line communications (PLC) include systems for communicating data over the same medium that is also used to transmit electric power to residences, buildings, and other premises, such as wires, power lines, or other conductors. In its simplest terms, PLC modulates communication signals over existing power lines. This enables devices to be networked without introducing any new wires or cables. This capability is extremely attractive across a diverse range of applications that can leverage greater intelligence and efficiency through networking. PLC applications include utility meters, home area networks, and appliance and lighting control. 
     PLC is a generic term for any technology that uses power lines as a communications channel. Various PLC standardization efforts are currently in work around the world. The different standards focus on different performance factors and issues relating to particular applications and operating environments. Two of the most well-known PLC standards are G3 and PRIME. G3 has been approved by the International Telecommunication Union (ITU). IEEE is developing the IEEE P1901.2 standard that is based on G3. Each PLC standard has its own unique characteristics. 
     Using PLC to communicate with utility meters enables applications such as Automated Meter Reading (AMR) and Automated Meter Infrastructure (AMI) communications without the need to install additional wires. Consumers may also use PLC to connect home electric meters to an energy monitoring device or in-home display monitor their energy consumption and to leverage lower-cost electric pricing based on time-of-day demand. 
     As the home area network expands to include controlling home appliances for more efficient consumption of energy, OEMs may use PLC to link these devices and the home network. PLC may also support home and industrial automation by integrating intelligence into a wide variety of lighting products to enable functionality such as remote control of lighting, automated activation and deactivation of lights, monitoring of usage to accurately calculate energy costs, and connectivity to the grid. 
     The manner in which PLC systems are implemented depends upon local regulations, characteristics of local power grids, etc. The frequency band available for PLC users depends upon the location of the system. In Europe, PLC bands are defined by the CENELEC (European Committee for Electrotechnical Standardization). The CENELEC-A band (3 kHz-95 kHz) is exclusively for energy providers. The CENELEC-B, C, D bands are open for end user applications, which may include PLC users. Typically, PLC systems operate between 35-90 kHz in the CENELEC A band using 36 tones spaced 1.5675 kHz apart. In the United States, the FCC has conducted emissions requirements that start at 535 kHz and therefore the PLC systems have an FCC band defined from 154-487.5 kHz using 72 tones spaced at 4.6875 kHz apart. In other parts of the world different frequency bands are used, such as the Association of Radio Industries and Businesses (ARIB)-defined band in Japan, which operates at 10-450 kHz, and the Electric Power Research Institute (EPRI)-defined bands in China, which operates at 3-90 kHz. 
     Different groups of nodes in a PLC network may use different technologies. For example, a first group of nodes may use a first protocol or standard to communicate, and a second group of nodes may use a second protocol or standard to communicate. Although the nodes using the different technologies may not attempt to communicate with each other, they may cause interference with each other on the PLC network. Depending upon the back-off method used in the channel access protocols for each technology, one technology may effectively block the other technology from the channel. 
     SUMMARY OF THE INVENTION 
     Embodiments of the invention support coexistence between two similar PLC technologies that rely on preamble detection to access a communication channel. The invention provides fairness to both technologies using a combination of a duty-cycle approach and a long-preamble approach ensures that both PLC technologies share the channel. The duty-cycle approach is non-intrusive in that it does not add to network overhead. The long-preamble approach may be intrusive by impacting network throughput. 
     In one embodiment, a system and method for supporting coexistence of different technologies on a power line communication network is disclosed. A power line communication device detects a coexistence preamble transmitted from a remote device on a channel in a PLC network. The device determines whether a threshold back-off duration has been reached. The device transmits a coexistence preamble sequence in response to a determination that the threshold back-off duration has been reached. The device may transmit a data frame on the channel after transmitting the coexistence preamble sequence. 
     The coexistence preamble sequence may comprise two or more repeated coexistence preambles. A size of the coexistence preamble sequence may be selected based upon a maximum packet size for the PLC device. The threshold back-off duration may be defined as a predetermined number N of coexistence Extended Interframe Space (cEIFS) durations for the PLC network. 
     The device may further determine that a first coexistence preamble sequence has been transmitted on the channel. The device then delays transmission of a second coexistence preamble sequence on the channel for at least a threshold back-off duration. 
     In another embodiment, a power line communication device monitors a channel occupancy duration during which devices transmit on a channel in a PLC network. The device determines when the channel occupancy duration exceeds a network duty cycle time (ndcTime). The device then backs off from the channel for a duty cycle Extended Interframe Space (dcEIFS) duration when the channel occupancy duration exceeds ndcTime . 
     The values for the ndcTime and dcEIFS parameters may be selected based upon channel access technologies used by PLC devices on the PLC network. The values of ndcTime and N may be selected so that ndcTime is less than the value of (N×EIFS). 
     In other embodiments, the value of ndcTime and (N×cEIFS) can be selected to give precedence to a particular approach. For example, ndcTime may be selected as less than N×cEIFS to give precedence to duty cycle approach, or N×cEIFS may be selected as less than ndcTime to give precedence to a long cycle approach. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus described the invention in general terms, reference will now be made to the accompanying drawings, wherein: 
         FIG. 1  is a diagram of a PLC system according to some embodiments. 
         FIG. 2  is a block diagram of a PLC device or modem according to some embodiments. 
         FIG. 3  is a block diagram of a PLC gateway according to some embodiments. 
         FIG. 4  is a block diagram of a PLC data concentrator according to some embodiments. 
         FIG. 5  is a schematic block diagram illustrating one embodiment of a system configured for point-to-point PLC. 
         FIG. 6  is a block diagram of an integrated circuit according to some embodiments. 
         FIG. 7  illustrates an example embodiment of a PLC network for a local utility PLC communications system. 
         FIG. 8  illustrates a network neighborhood having devices that use two different technology parameters. 
         FIG. 9  illustrates an example PLC network having PLC nodes using a first technology and PLC nodes using a second technology. 
         FIG. 10  illustrates a long coexistence preamble sequence according to one embodiment. 
         FIG. 11  illustrates an example method that may be used to determine the transmission of a long coexistence preamble sequence. 
         FIG. 12  illustrates a method for using a network duty cycle time by a power line communication device according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The invention now will be described more fully hereinafter with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. One skilled in the art may be able to use the various embodiments of the invention. 
       FIG. 1  illustrates a power line communication network according to some embodiments. Medium voltage (MV) power lines  103  from subnode  101  typically carry voltage in the tens of kilovolts range. Transformer  104  steps the MV power down to low voltage (LV) power on LV lines  105 , carrying voltage in the range of 100-240 VAC. Transformer  104  is typically designed to operate at very low frequencies in the range of  50 - 60  Hz. Transformer  104  does not typically allow high frequencies, such as signals greater than  100  KHz, to pass between LV lines  105  and MV lines  103 . LV lines  105  feed power to customers via meters or nodes  106   a - n , which are typically mounted on the outside of residences  102   a - n . Although referred to as “residences,” premises  102   a - n  may include any type of building, facility, electric vehicle charging node, or other location where electric power is received and/or consumed. A breaker panel, such as panel  107 , provides an interface between meter  106   n  and electrical wires  108  within residence  102   n . Electrical wires  108  deliver power to outlets  110 , switches  111  and other electric devices within residence  102   n.    
     The power line topology illustrated in  FIG. 1  may be used to deliver high-speed communications to residences  102   a - n . In some implementations, power line communications modems or gateways  112   a - n  may be coupled to LV power lines  105  at meter  106   a - n . PLC modems/gateways  112   a - n  may be used to transmit and receive data signals over MV/LV lines  103 / 105 . Such data signals may be used to support metering and power delivery applications (e.g., smart grid applications), communication systems, high speed Internet, telephony, video conferencing, and video delivery, to name a few. By transporting telecommunications and/or data signals over a power transmission network, there is no need to install new cabling to each subscriber  102   a - n . Thus, by using existing electricity distribution systems to carry data signals, significant cost savings are possible. 
     An illustrative method for transmitting data over power lines may use a carrier signal having a frequency different from that of the power signal. The carrier signal may be modulated by the data, for example, using an OFDM technology or the like described, for example, G3 -PLC standard. 
     PLC modems or gateways  112   a - n  at residences  102   a - n  use the MV/LV power grid to carry data signals to and from PLC data concentrator or router  114  without requiring additional wiring. Data concentrator or router  114  may be coupled to either MV line  103  or LV line  105 . Modems or gateways  112   a - n  may support applications such as high-speed broadband Internet links, narrowband control applications, low bandwidth data collection applications, or the like. In a home environment, for example, modems or gateways  112   a - n  may further enable home and building automation in heat and air conditioning, lighting, and security. Also, PLC modems or gateways  112   a - n  may enable AC or DC charging of electric vehicles and other appliances. An example of an AC or DC charger is illustrated as PLC device  113 . Outside the premises, power line communication networks may provide street lighting control and remote power meter data collection. 
     One or more PLC data concentrators or routers  114  may be coupled to control center  130  (e.g., a utility company) via network  120 . Network  120  may include, for example, an IP-based network, the Internet, a cellular network, a WiFi network, a WiMax network, or the like. As such, control center  130  may be configured to collect power consumption and other types of relevant information from gateway(s)  112  and/or device(s)  113  through concentrator(s)  114 . Additionally or alternatively, control center  130  may be configured to implement smart grid policies and other regulatory or commercial rules by communicating such rules to each gateway(s)  112  and/or device(s)  113  through concentrator(s)  114 . 
       FIG. 2  is a block diagram of PLC device  113  according to some embodiments. As illustrated, AC interface  201  may be coupled to electrical wires  108   a  and  108   b  inside of premises  112   n  in a manner that allows PLC device  113  to switch the connection between wires  108   a  and  108   b  off using a switching circuit or the like. In other embodiments, however, AC interface  201  may be connected to a single wire  108  (i.e., without breaking wire  108  into wires  108   a  and  108   b ) and without providing such switching capabilities. In operation, AC interface  201  may allow PLC engine  202  to receive and transmit PLC signals over wires  108   a - b . In some cases, PLC device  113  may be a PLC modem. Additionally or alternatively, PLC device  113  may be a part of a smart grid device (e.g., an AC or DC charger, a meter, etc.), an appliance, or a control module for other electrical elements located inside or outside of premises  112   n  (e.g., street lighting, etc.). 
     PLC engine  202  may be configured to transmit and/or receive PLC signals over wires  108   a  and/or  108   b  via AC interface  201  using a particular frequency band. In some embodiments, PLC engine  202  may be configured to transmit OFDM signals, although other types of modulation schemes may be used. As such, PLC engine  202  may include or otherwise be configured to communicate with metrology or monitoring circuits (not shown) that are in turn configured to measure power consumption characteristics of certain devices or appliances via wires  108 ,  108   a , and/or  108   b . PLC engine  202  may receive such power consumption information, encode it as one or more PLC signals, and transmit it over wires  108 ,  108   a , and/or  108   b  to higher-level PLC devices (e.g., PLC gateways  112   n , data aggregators  114 , etc.) for further processing. Conversely, PLC engine  202  may receive instructions and/or other information from such higher-level PLC devices encoded in PLC signals, for example, to allow PLC engine  202  to select a particular frequency band in which to operate. 
       FIG. 3  is a block diagram of PLC gateway  112  according to some embodiments. As illustrated in this example, gateway engine  301  is coupled to meter interface  302 , local communication interface  304 , and frequency band usage database  304 . Meter interface  302  is coupled to meter  106 , and local communication interface  304  is coupled to one or more of a variety of PLC devices such as, for example, PLC device  113 . Local communication interface  304  may provide a variety of communication protocols such as, for example, ZigBee, Bluetooth, Wi-Fi, Wi-Max, Ethernet, etc., which may enable gateway  112  to communicate with a wide variety of different devices and appliances. In operation, gateway engine  301  may be configured to collect communications from PLC device  113  and/or other devices, as well as meter  106 , and serve as an interface between these various devices and PLC data concentrator  114 . Gateway engine  301  may also be configured to allocate frequency bands to specific devices and/or to provide information to such devices that enable them to self-assign their own operating frequencies. 
     In some embodiments, PLC gateway  112  may be disposed within or near premises  102   n  and serve as a gateway to all PLC communications to and/or from premises  102   n . In other embodiments, however, PLC gateway  112  may be absent and PLC devices  113  (as well as meter  106   n  and/or other appliances) may communicate directly with PLC data concentrator  114 . When PLC gateway  112  is present, it may include database  304  with records of frequency bands currently used, for example, by various PLC devices  113  within premises  102   n . An example of such a record may include, for instance, device identification information (e.g., serial number, device ID, etc.), application profile, device class, and/or currently allocated frequency band. As such, gateway engine  301  may use database  305  in assigning, allocating, or otherwise managing frequency bands assigned to its various PLC devices. 
       FIG. 4  is a block diagram of PLC data concentrator or router  114  according to some embodiments. Gateway interface  401  is coupled to data concentrator engine  402  and may be configured to communicate with one or more PLC gateways  112   a - n . Network interface  403  is also coupled to data concentrator engine  402  and may be configured to communicate with network  120 . In operation, data concentrator engine  402  may be used to collect information and data from multiple gateways  112   a - n  before forwarding the data to control center  130 . In cases where PLC gateways  112   a - n  are absent, gateway interface  401  may be replaced with a meter and/or device interface (now shown) configured to communicate directly with meters  116   a - n , PLC devices  113 , and/or other appliances. Further, if PLC gateways  112   a - n  are absent, frequency usage database  404  may be configured to store records similar to those described above with respect to database  304 . 
       FIG. 5  is a schematic block diagram illustrating one embodiment of a system  500  configured for point-to-point PLC. The system  500  may include a PLC transmitter  501  and a PLC receiver  502 . For example, a PLC gateway  112  may be configured as the PLC transmitter  501  and a PLC device  113  may be configured as the PLC receiver  502 . Alternatively, the PLC device  113  may be configured as the PLC transmitter  501  and the PLC gateway  112  may be configured as the PLC receiver  502 . In still a further embodiment, the data concentrator  114  may be configured as either the PLC transmitter  501  or the PLC receiver  502  and configured in combination with a PLC gateway  112  or a PLC device  113  in a point-to-point system  500 . In still a further embodiment, a plurality of PLC devices  113  may be configured to communicate directly in a point-to-point PLC system  500  as described in  FIG. 5 . Additionally, the subnode  101  may be configured in a point-to-point system  500  as described above. On of ordinary skill in the art will recognize a variety of suitable configurations for the point-to-point PLC system  500  described in  FIG. 5 . 
       FIG. 6  is a block diagram of a circuit for implementing the transmission of multiple beacon frames using different modulation techniques on each tone mask in a PLC network according to some embodiments. In some cases, one or more of the devices and/or apparatuses shown in  FIGS. 1-5  may be implemented as shown in  FIG. 6 . In some embodiments, processor  602  may be a digital signal processor (DSP), an application specific integrated circuit (ASIC), a system-on-chip (SoC) circuit, a field-programmable gate array (FPGA), a microprocessor, a microcontroller, or the like. Processor  602  is coupled to one or more peripherals  604  and external memory  603 . In some cases, external memory  603  may be used to store and/or maintain databases  304  and/or  404  shown in  FIGS. 3 and 4 . Further, processor  602  may include a driver for communicating signals to external memory  603  and another driver for communicating signals to peripherals  604 . Power supply  601  provides supply voltages to processor  602  as well as one or more supply voltages to memory  603  and/or peripherals  604 . In some embodiments, more than one instance of processor  602  may be included (and more than one external memory  603  may be included as well). 
     Peripherals  604  may include any desired circuitry, depending on the type of PLC system. For example, in an embodiment, peripherals  604  may implement local communication interface  303  and include devices for various types of wireless communication, such as Wi-Fi, ZigBee, Bluetooth, cellular, global positioning system, etc. Peripherals  604  may also include additional storage, including RAM storage, solid-state storage, or disk storage. In some cases, peripherals  604  may include user interface devices such as a display screen, including touch display screens or multi-touch display screens, keyboard or other input devices, microphones, speakers, etc. 
     External memory  603  may include any type of memory. For example, external memory  603  may include SRAM, nonvolatile RAM (NVRAM, such as “flash” memory), and/or dynamic RAM (DRAM) such as synchronous DRAM (SDRAM), double data rate (DDR, DDR2, DDR3, etc.) SDRAM, DRAM, etc. External memory  603  may include one or more memory modules to which the memory devices are mounted, such as single inline memory modules (SIMMs), dual inline memory modules (DIMMs), etc. 
       FIG. 7  illustrates an example embodiment of a PLC network  700  for a local utility PLC communications system. Network  700  includes LV nodes  702   a - n  and each of the nodes  702   a - n  is connected to MV power line  720  through a corresponding transformer  710   a - n  and LV line  706   a - n . Router, or modem,  714  is also connected to MV power line  720 . A sub-network  728 , or neighborhood  728 , may be represented by the combination of nodes  702   a - n  and router  714 . Master router  712  and router  716  are also connected to MV line  720 , which is powered by power grid  722 . Power grid  722  represents the high voltage power distribution system. 
     Master router  712  may be the gateway to telecommunications backbone  724  and local utility, or control center,  726 . Master router  712  may transmit data collected by the routers to the local utility  726  and may also broadcast commands from local utility  726  to the rest of the network. The commands from local utility  726  may require data collection at prescribed times, changes to communication protocols, and other software or communication updates. 
     During UL communications, the nodes  702   a - n  in neighborhood  728  may transmit usage and load information (“data”) through their respective transformer  710   a - n  to the MV router  714 . In turn, router  714  forwards this data to master router  712 , which sends the data to the utility company  726  over the telecommunications backbone  724 . During DL communications (router  714  to nodes  702   a - n ) requests for data uploading or commands to perform other tasks are transmitted. 
     In accordance with various embodiments, nodes  702   a - n  may be devices using different standards or protocols that operate together in coexistence. In PLC networks where there are several different devices with different technology parameters (e.g., devices using one of IEEE P1901.2 FCC-low band, IEEE P1901.2 CEN-A, and IEEE P1901.2 FCC, G.hnem), a common back-off time for all devices  702   a - n  in the network-coexistence Extended Inter Frame Space (cEIFS)—may be defined. A device  702   n  will back-off for a cEIFS interval if the device  702   n  detects a coexistence preamble but does not detect the device  702   n  ′ s own native preamble. In one embodiment, cEIFS may be a Personal Area Network (PAN) -specific parameter. 
     In other embodiments, the system may include devices operating according to different standards or protocols that all communication on FCC-assigned frequencies. For example, the system may include G3 devices that operate according to ITU or IEEE standards, such as IEEE P1901.2. The system may also include devices that operate according to the PRIME standard. The present embodiments may also enable coexistence between these devices. 
     In a network with devices operating with two or more different technology parameters, devices from one technology may dominate network access. 
     Table 1 illustrates example band plans that may be used by nodes having different technologies. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Band-Plan 
                 Band-Frequencies 
               
               
                   
               
             
            
               
                 1 
                 IEEE P1901.2 FCC Band 
                 154.6875 kHz-487.5 kHz 
               
               
                 2 
                 ITU-G3 ARM Band 
                 154.6875 kHz-403 kHz   
               
               
                 3 
                 ITU-G3 FCC1 Band 
                 154.6875 kHz-262 kHz   
               
               
                 4 
                 ITU-G.hnem FCC Band 
                   35 kHz-480 kHz 
               
               
                 5 
                 IEEE P1901.2 FCC Multitone 36-1 
                 154.6875 kHz-318 kHz   
               
               
                 6 
                 IEEE P1901.2 FCC Multitone 36-2 
                    323 kHz-487.5 kHz 
               
               
                 7 
                 IEEE P1901.2 FCC Low Band 
                     37.5 kHz-121.875 kHz 
               
               
                 8 
                 IEEE/G3 CEN-A 
                   35 kHz-90 kHz 
               
               
                 9 
                 PRIME CEN-A 
                     kHz-88.8 kHz 
               
               
                   
               
            
           
         
       
     
       FIG. 8  illustrates a network neighborhood  800  having devices  801 ,  802  operating with two different technology parameters. Devices  801  communicate with technology 1 parameters, and devices  802  communicate with technology  2  parameters. It may arise that devices using one technology may dominate network access. For example, communication may be dominated by devices  801  using technology  1  under the following conditions: 
     a) if there is a presence of more devices  801  using technology  1  in network neighborhood  800 ; or 
     b) if cEIFS is a large value resulting in the devices  802  using technology  2  continuously backing off. 
     Although the adaptive back-off scheme in the IEEE P1901.2 standard penalizes a transmitter that wins the channel consecutively for several transmissions by choosing the maximum back-off value, there are still scenarios for which fair channel access mechanisms are required. 
     In one scenario, fair channel access mechanisms are required when there are multiple transmitters  801  using the same technology in a particular neighborhood  800  compared to few nodes  802  using an alternate technology. In this scenario, nodes  801  (using the same technology) may take turns accessing the channel and consequently will never encounter the state where a particular node  801  gets channel access consecutively. However, it is likely that these several nodes  801  together may have acquired channel access consecutively. Mechanisms are needed to enable the alternate technology nodes  802  to fairly contend for the channel if this scenario is encountered. 
     In other scenarios, a generic fair channel access methodology is needed to address technologies (e.g., other than IEEE P1901.2) that may not necessarily penalize the winning transmitter after several successful channel accesses. The mechanisms may be agnostic of the underlying channel access mechanism for a specific technology. 
       FIG. 9  illustrates an example PLC network  900  having PLC nodes  901  using a first technology and PLC nodes  902  using a second technology. As described in connection with  FIG. 8 , if the technology  1  nodes  901  outnumber the technology  2  nodes  902 , then the technology  1  nodes  901  may dominate the channel on power line  903  thereby preventing technology  2  nodes  902  from accessing the channel. 
     A hybrid solution based upon a combination of a long coexistence preamble and a defined network duty cycle is proposed to address this situation. 
     Long Coexistence Preamble Approach 
     A long coexistence preamble sequence may be defined. An example of a long coexistence preamble sequence  1000  is illustrated in  FIG. 10 . The long coexistence preamble sequence  1000  consists of m repeated preambles (e.g., syncC symbols)  1001   a - m . The value of m can be selected such that the coexistence sequence  1000  is as large as the maximum packet size supported by a selected technology. The syncC symbol may be defined as any appropriate synchronization symbol, such as one or more of the syncP and/or syncM synchronization symbols defined in the IEEE P1901.2 standard. Alternatively, the syncC symbol may be a generic synchronization symbol across different technologies and may correspond to either a chirp signal or known sequence of +/−1&#39;s. 
       FIG. 11  illustrates an example method that may be used to determine the transmission of a long coexistence preamble sequence. 
     In step  1101 , devices using a first technology (technology  1 ) and a second technology (technology  2 ) attempt to access a PLC channel using the appropriate access method for their respective technologies. 
     In step  1102 , a device using technology  2  will back off for an additional duration of cEIFS, if the device detects a coexistence preamble and does not detect its native preamble while in cEIFS period. 
     In step  1103 , if a device from technology  2  has attempted to access the channel N times for transmission and has backed off for N cEIFS durations, then the device may transmit a coexistence preamble sequence, such as the coexistence preamble  1000  defined above and illustrated in  FIG. 10 . Transmission of the coexistence preamble sequence is a way of “requesting” channel access from devices of the different technologies (e.g., technology  1 ) that are using the channel. The idea here is that if the coexistence preamble sequence is long enough, then there will be a time slot in which only the coexistence preamble sequence is present in the channel. This will result in the devices that are using technology  1  to back off (for a cEIFS interval) and thereby “releasing” the channel. 
     In step  1104 , the technology  2  device may transmit a data frame after the long coexistence preamble sequence. 
     In step  1105 , subsequent channel accesses may be subject to each respective technology&#39;s channel access mechanisms. For example, technology  1  nodes may contend after the cEIFS duration. 
     In step  1106 , on receiving a long preamble (e.g., more than  2  coexistence preambles), all service nodes irrespective of the technology used will not send any other long preambles for the next N×cEIFS. This ensures that there is no more than  1  long preamble in a sensing region every N×cEIFS. 
     Duty Cycle 
     A Network Duty Cycle (ndcTime) parameter may be defined as the maximum allowed duration for nodes of the PLC network to occupy the channel. After the ndcTime, all nodes of that network will backoff the channel for a duty cycle cEIFS (dcEIFS) before being allowed to transmit again. All technologies will have the same dcEIFS. 
     The ndcTime and dcEIFS parameters may be configurable to allow regional and band settings that best match local requirements. 
     Note that if the ndcTime duration is on the order of a few transmissions, then there may be a loss in throughput for nodes using one type of technology. On the other hand, if the ndcTime duration is too large, then there may not be a guarantee that nodes using another type of technology will have a transmission to be made during that time. Hence an optimum value should be selected for the ndcTime parameter. 
       FIG. 12  illustrates a method for using a network duty cycle time by a power line communication device according to one embodiment. In step  1201 , a channel occupancy duration is monitored. The channel occupancy duration represents a time during which devices transmit on a channel in a PLC network. In step  1202 , the PLC device determines when the channel occupancy duration exceeds a network duty cycle time (ndcTime). In step  1203 , the PLC device backs off from the channel for a duty cycle Extended Interframe Space (dcEIFS) duration when the channel occupancy duration exceeds the ndcTime. 
     Overall Solution 
     A node may be capable of performing either or both of the above mentioned solutions. Also, it is recommended to choose the ndcTime and N parameters such that ndcTime&lt;N×cEIFS. 
     It is to be noted that if the duty cycling with ndcTime allows a technology  2  node to get access to channel, then the node will not be needed to transmit a long preamble (i.e., a N×cEIFS time of non-access to channel will not happen). 
     Also, if even after duty cycling, a technology  2  node does not get access to the channel, then that node will send a long preamble after N×cEIFS. 
     The values of the ndcTime and N may be selected depending upon the types of technology used by the nodes in the network. The rate at which these solutions are used can be controlled by the choice of these parameters at deployment. At deployment, if it is intended that the duty based solution alone is to be used, then the value of N can be set to a large value. On the other hand, at deployment the duty cycle approach can be disabled by choosing ndcTime&gt;N×cEIFS. 
     Many modifications and other embodiments of the invention(s) will come to mind to one skilled in the art to which the invention(s) pertain having the benefit of the teachings presented in the foregoing descriptions, and the associated drawings. Therefore, it is to be understood that the invention(s) are not to be limited to the specific embodiments disclosed. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.