Abstract:
A communication system is disclosed which includes: at least one power line communication device configured to be connected with another power line communication device via a common power line for providing a commercial alternate-current power supply; and a communication terminal configured to include a modem for power line communication and a coil for exchanging power line communication signals with an external entity through electromagnetic coupling, the communication terminal sending and receiving the signals to and from the external entity through electromagnetic coupling between the coil and the power line.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to Japanese Patent Application JP 2007-308300 filed in the Japan Patent Office on Nov. 29, 2007, the entire contents of which is being incorporated herein by reference. 
       BACKGROUND 
       [0002]    The present application relates to a communication system and a communication apparatus for conducting power line communication when connected to household outlets. More particularly, the present application relates to a communication system and a communication apparatus for allowing mobile devices such as personal digital assistants (PDAs) and cellular phones operating without using a commercial alternate current (AC) power supply to carry out power line communication therebetween. 
         [0003]    Recent years have witnessed the commercialization of power line communication (PLC) as convenient means to set up a local area network (LAN) in private houses or like situations. According to the PLC scheme, devices which are powered by power lines and which have a PLC capability can multiplex their communication signals on the power lines for communication with other devices having the same capability. 
         [0004]    Wireless LAN has gained widespread acceptance as simple means to establish a LAN. Under radio law, this scheme has been subject to limited levels of transmission output to avoid interference with other radio systems and related devices. That means the wireless LAN setup has difficulty in bringing its radio waves to the configured devices across walls under the same roof. On the other hand, the PLC setup uses the existing power lines to permit communication between the connected devices in separate rooms as long as the devices are plugged into electrical outlets on the walls. The PLC scheme thus makes it possible to implement a LAN for high-speed communication at transmission rates of at least 100 Mbps without establishing an Ethernet (registered trademark) inside the building. 
         [0005]      FIG. 8  is a schematic view showing an ordinary home network system based on PLC. In  FIG. 8 , reference numeral  100  denotes a household power line. Reference numerals  101  and  106  stand for household electrical outlets;  102  and  107  for AC plugs; and  103  and  108  for PLC modems (PLC modem  103  acts as the master device). Reference numeral  109  stands for a host such as a personal computer (PC);  104  for an optical line terminal device; and  105  for the Internet. The optical line terminal device  104  may be replaced by an asymmetric digital subscriber line (ADSL) modem. 
         [0006]    The PLC modems  103  and  108  communicate with each other via the power line  100 . This allows the PC  109  to connect to the Internet  104  by way of the optical line terminal device  104 . 
         [0007]    Systems have been proposed (such as one disclosed by Japanese Patent Laid-Open No. 2005-143026) which monitor and control household equipment using PLC. This type of system involves providing home-bound devices including household electrical appliances with PLC capabilities, getting a master device (e.g., PC) to monitor and control the connected devices, and allowing the master device to be further accessed from the outside via a public communication network for such monitoring and control operations. 
         [0008]    Since PLC involves the use of power lines as transmission channels, the network configuration utilizing the existing power line layout is based on the so-called bus topology. That is, all communication devices connected by PLC to the household power lines share a bandwidth on a time-sharing basis. Whereas the typical system configuration shown in  FIG. 8  has two PLC modems, a plurality of PLC modems may be configured for communication therebetween. 
         [0009]    As shown in  FIG. 8 , the ordinary power line communication system basically utilizes a commercial AC power supply such as a desktop PC as its primary drive source. The system is then used by the connected devices each furnished with an AC plug capable of plugging into an AC outlet. In other words, mobile devices such as PDAs and cellular phones operating off batteries are incapable of communicating with one another by PLC. In such cases, each mobile device equipped with a wireless LAN capability needs to be connected to the PLC system via an access point, or needs to plug into an AC outlet by way of a PLC modem or an AC adapter. Such a roundabout practice can turn out to be quite inconvenient. 
       SUMMARY 
       [0010]    The present application has been made in view of the above circumstances and provides a communication system and a communication apparatus for advantageously conducting power line communication when connected to commercial AC electrical outlets. The present application also relates to providing a communication system and a communication apparatus for allowing mobile devices such as PDAs and cellular phones not utilizing a commercial AC power supply to conduct power line communication therebetween. 
         [0011]    In an embodiment, there is provided a communication system including: at least one power line communication device configured to be connected with another power line communication device via a common power line for providing a commercial alternate-current power supply; and a communication terminal configured to include a modem for power line communication and a coil for exchanging power line communication signals with an external entity through electromagnetic coupling, the communication terminal sending and receiving the signals to and from the external entity through electromagnetic coupling between the coil and the power line. 
         [0012]    In this specification, the term “system” refers to a logical configuration of a plurality of component devices or functional modules configured to implement specific functions. Each of the devices or functional modules may or may not be housed in a single enclosure. 
         [0013]    According to another embodiment, there is provided a communication system including: at least one power line communication device configured to be connected with another power line communication device via a common power line for providing a commercial alternate-current power supply; a communication terminal configured to include a modem for power line communication and a first coil for exchanging power line communication signals with an external entity through electromagnetic coupling; and a coupling device configured to be connected with the power line and include a filter for attenuating alternate-current components on the power line and a second coil installed upstream of the filter; wherein the communication terminal conducts proximity communication with another communication terminal using the magnetic coupling effect occurring between the first and the second coils in the proximity of the coupling device. 
         [0014]    According to a further embodiment, there is provided a communication system including: a plurality of communication terminals each configured to include a modem for power line communication and a first coil for exchanging power line communication signals with an external entity through electromagnetic coupling; and a coupling device configured to be connected with a power line and include a plurality of second coils laid out in a two-dimensional array connected to the power line via a filter for attenuating alternate-current components on the power line; wherein the plurality of communication terminals conduct proximity communication with one another using the magnetic coupling effect occurring between each of the first coils and each of the second coils in the proximity of the coupling device. 
         [0015]    According to further embodiment, there is provided a communication system including: a first and a second communication apparatus each configured to include a modem for power line communication and a coil for exchanging power line communication signals with an external entity through electromagnetic coupling; wherein the first and the second communication apparatuses conduct proximity communication with each other using the electromagnetic coupling effect occurring when the coil of the first communication apparatus is placed in proximity to the coil of the second communication apparatus in such a manner that the coils are opposed to each other. 
         [0016]    The power line communication technology has been commercialized as means to set up a LAN easily inside the household or other buildings. The devices connected to the network can communicate with one another when plugged into AC outlets on the walls of separate rooms. High-speed communications at 100 Mbps or higher are made available between the configured devices. 
         [0017]    Basically, the traditional power line communication system uses as its principal drive source a commercial AC power supply such as a desktop PC, and includes devices with AC plugs capable of plugging into AC outlets. It follows that mobile devices including PDAs and cellular phones with no means to tap the commercial AC power supply have difficulty in connecting to the PLC system. 
         [0018]    By contrast, the communication system has each of the configured mobile devices furnished with a modem for power line communication and a coil for exchanging power line communication signals with an external entity through electromagnetic coupling. The coil of such a mobile device receives leakage signals from the power line of some other PLC device for communication with the opposite party by use of the electromagnetic coupling effect occurring between the coil and the power line. 
         [0019]    Alternatively, a coupling device may be connected to the power line, the device including a filter for attenuating AC components on the power line and a coil installed downstream of the filter to permit electromagnetic coupling with the coil of a mobile device. In the proximity of the coupling device, the mobile device can take part in the power line communication setup through proximity communication with the coupling device. 
         [0020]    The coupling device is simply structured with a filter and a coil downstream thereof. The coil may be in the form of an electromagnetic coupling sheet made up of a plurality of coils arranged in a two-dimensional array. 
         [0021]    Mobile devices may each be equipped with a modem for power line communication and a coil for exchanging power line communication signals with an external entity through electromagnetic coupling. Such mobile devices may conduct proximity communication with one another directly by having their coils positioned opposite to one another, without recourse to power line communication channels. 
         [0022]    The present application, as outlined above, provides a communication system and a communication apparatus for ensuring power line communication advantageously when connected to common AC outlets. 
         [0023]    According to an embodiment, mobile devices including PDAs and cellular phones can directly participate in a PLC network. Such mobile devices can then communicate with external entities through PLC in places not reached by wireless LAN signals. 
         [0024]    The coupling device, as outlined above, is simply structured with the filter and the coil downstream thereof. The coil may be in the form of an electromagnetic coupling sheet made up of a plurality of coils arranged in a two-dimensional array. In this setup, the communicable area is in the proximity of the surface of the electromagnetic coupling sheet. With its communicable area much more limited than that of wireless LANs, the coupling device runs little danger of getting eavesdropped and provides enhanced levels of security. When a plurality of mobile devices each equipped with the PLC modem and coil are placed on the electromagnetic coupling sheet, the sheet allows the devices to communicate with one another. 
         [0025]    Each mobile device furnished with the PLC modem and coil can communicate with its opposite party when its coil picks up leakage signals from the power line of another PLC device. Signal exchanges based on the electromagnetic coupling effect between the coil and the power line permit communication without the intervention of the coupling device such as the electromagnetic coupling sheet. This arrangement makes it possible for mobile devices to conduct communication in diverse locations. 
         [0026]    Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0027]      FIG. 1  is a schematic view showing a typical configuration of a home network system practiced according to an embodiment; 
           [0028]      FIG. 2  is a schematic view showing an internal structure of an electromagnetic coupling sheet; 
           [0029]      FIG. 3  is a block diagram showing an internal structure of a PLC modem; 
           [0030]      FIG. 4  is a block diagram showing an internal structure of a PDA; 
           [0031]      FIG. 5  is a schematic view depicting steps to be taken by PLC modems for communication; 
           [0032]      FIG. 6  is a schematic view showing a setup where a PDA conducts communication using leakage power from a power line without recourse to a dedicated electromagnetic coupling sheet; 
           [0033]      FIG. 7  is a schematic view showing how mobile devices communicate with each other without the intervention of power line communication channels; and 
           [0034]      FIG. 8  is a schematic view showing a traditional home network system based on PLC. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    An embodiment of the present application will now be described in detail with reference to the accompanying drawings.  FIG. 1  schematically shows a typical configuration of a home network system according to embodiment. 
         [0036]    The system in  FIG. 1  and the system in  FIG. 8  are similar as follows. For example, a power line  100  is assumed to be installed in the household. An AC plug  107  at the tip of the power cable of a PLC modem  108  attached to a personal computer  109  is connected to a home AC outlet  106 . The connection allows the personal computer  109  to take part in the home PLC network. An AC plug  102  at the tip of the power cable of an optical line terminal device (or an ADSL modem)  104  is plugged into a home AC outlet  101 . The latter connection allows the home PLC network to connect with the Internet  105 . 
         [0037]    A difference between the system of  FIG. 1  and the system of  FIG. 8  is that a PDA  205  has joined the PLC network as a communication device taking part in the system as embodied in  FIG. 1 . 
         [0038]    Since the PDA  205  does not operate on commercial AC power, it cannot have its putative AC plug connected to an AC outlet in order to participate in the PLC network. Instead, the PDA  205  includes a PLC modem and a coil for sending and receiving signals through electromagnetic coupling (to be discussed later). An electromagnetic coupling sheet  202  provides an environment of electromagnetic coupling which allows the PDA  205  to become part of the PLC network. The electromagnetic coupling sheet  202  includes a filter for attenuating AC components on the power line and a coil connected downstream of the filter for electromagnetic coupling purposes (to be discussed later). When the coil inside the PDA  205  is placed in the proximity of the coil in the sheet  202 , the electromagnetic coupling effect occurs between the coils allowing the PDA  205  to send and receive PLC signals. The band for use in power line communication ranges typically from 2 to 30 MHz. A wideband setup covering that frequency band for electromagnetic coupling is demanded. 
         [0039]    The PDA  205  is used placed on the electromagnetic coupling sheet  202 . A plurality of mobile devices may be placed on the electromagnetic coupling sheet  202  depending on the latter&#39;s size. Each of these mobile devices may then communicate with another PLC modem. It is also possible for these mobile devices to communicate with one another when placed on the electromagnetic coupling sheet  202  (to be discussed later; see  FIG. 7 ). 
         [0040]    The electromagnetic sheet  202  is made up of a high-pass filter (HPF)  203  for cutting (or attenuating) AC components (50 to 60 Hz) from the AC line, and a coil  204  for effecting electromagnetic induction with the coil of a mobile device. 
         [0041]    By way of the electromagnetic coupling sheet  202 , power line  100 , and PLC modems  103  and  108 , the PDA  205  as a mobile device can thus conduct communication using PLC signals. It is also possible for the PDA  205  to connect to the Internet  105  via the optical line terminal device  104  or to communicate with the personal computer  109  participating in the PLC network. 
         [0042]    Although the foregoing description showed the mobile device and the electromagnetic coupling sheet to be connected with one another through a magnetic field occurring therebetween, an electric field is also considered to play a significant role in the connection. Thus the scope of the present application is not limited by the effect of electromagnetic coupling. 
         [0043]      FIG. 2  schematically shows an internal structure of the electromagnetic coupling sheet  202 . Reference numeral  203  represents a high-pass filter and  204  denotes for a coil. The high-pass filter  203  is constituted by a power transformer  300  and two capacitors  301  and  302 . These components form a balanced input/output high-pass filter. The terminals of the capacitors  301  and  302  are connected to the power line  100 . 
         [0044]    Orthogonal frequency division multiplex (OFDM) is utilized extensively as the modulation method for PLC. Under the OFDM modulation method, the frequencies of different carriers are established in such a manner that their subcarriers will be orthogonal to one another within each symbolic interval. The subcarriers being orthogonal to one another signify that the spectrum peak point of a given subcarrier coincides invariably with that of another subcarrier so that no cross talk occurs even if the bands of adjacent subcarriers are close enough to overlap with one another. Because outgoing data is distributed among a plurality of carriers with their frequencies orthogonal to one another, each carrier is assigned a narrowband. This method provides very high levels of efficiency in frequency utilization. 
         [0045]    Reference numeral  303  in  FIG. 2  denotes a waveform of a PLC signal sent over the power line  100 . It will be appreciated that an OFDM signal is multiplexed onto the AC signal. When the PLC signal passes through the high-pass filter  203 , the AC components of 50 to 60 Hz are removed from the signal. The result is an AC component-free OFDM signal indicated by reference numeral  304 . The OFDM signal from the electromagnetic coupling sheet  202  (i.e., outgoing signal from a PDA  20 ) moves in the reverse direction: when passing through the high-pass filter  203 , the OFDM signal is multiplexed onto the AC signal for transmission to the opposite PLC modem in communication. 
         [0046]      FIG. 3  shows an internal structure of a PLC modem  400 . The PLC modem  400  is representative of the PLC modems  103  and  108  in  FIG. 1 . Reference numeral  401  stands for an AC plug;  402  for a power supply section that rectifies AC power to DC power;  403  for a high-pass filter;  404  for a coupling section that couples outgoing waves with incoming waves;  405  for a reception section;  406  for a transmission section;  407  for a baseband processing section that modulates and demodulates the OFDM signal while effecting communication control; and 408 for an interface section that carries out interfacing processes such as those of the Ethernet (registered trademark). 
         [0047]    The PLC signal received by the AC plug  401  is sent to the high-pass filter  403  whereby the AC components of 50 to 60 Hz are removed from the signal. The filtered PLC signal is then forward through the coupling section  404  to the reception section  405  for amplification. The amplified signal from the reception section  405  is sent to the baseband processing section  407 . The baseband processing section  407  subjects the received signal to analog/digital (A/D) conversion followed by OFDM demodulation for conversion of the signal into digital data. 
         [0048]    Data coming over the Ethernet (registered trademark) is forwarded through the interface section  408  to the baseband processing section  407  for OFDM modulation and digital/analog (D/A) conversion. Having undergone the processing by the baseband processing section  407 , the data becomes a PLC signal that is passed on to the transmission section  406 . The PLC signal is amplified by the transmission section  406  before being multiplexed onto an AC power signal by way of the coupling section  404  and high-pass filter  403 . The multiplexed signal is sent onto the power line  100  through the AC plug  401 . 
         [0049]    The baseband processing section  407  also performs machine access control (MAC) processes including framing, de-framing, error correction, and retransmission. 
         [0050]    At the PLC modem  400 , a master-slave changeover is needed. A switching section designated by reference numeral  410  allows the user manually to switch between the master and the slave settings. The PLC modem acting as the master station transmits beacon signals intermittently. Each PLC modem serving as a slave station checks the beam signals to determine the availability of communication and other kinds of information. The master station is valid in the case where Qos (quality of service) is demanded. Where a plurality of PLC modems are interconnected in an autonomous distributed control setup, there is no need for defining the master-slave relationship therebetween. 
         [0051]      FIG. 4  shows an internal structure of the PDA  205 . In  FIG. 4 , reference numeral  500  denotes a PLC modem section. The PLC modem section  500  may be in the form of either a built-in module or a detachable card such as a compact flash card. 
         [0052]    Reference numeral  206  represents a coil for effecting electromagnetic coupling with the coil  204  of the electromagnetic coupling sheet  202 . Reference numeral  501  denotes a terminal section  501  (i.e., body of the PDA). The structure of the PDA body is not relevant to the scope of the present application and thus will not be discussed further. The PLC modem section  500  is interfaced with the terminal section  501  through a bus connection if the PLC modem section  500  is a built-in section or through the use of a compact flash interface if the PLC modem section  500  is a detachable card. Reference numeral  502  represents a battery section and  503  represents a communication status display section by LED or the like. 
         [0053]    The PLC signal received by the coil  206  is sent through the coupling section  404  to the reception section  405  for amplification. The amplified PLC signal is forwarded to the baseband processing section  407  for A/D conversion followed by OFDM demodulation, whereby the PLC signal is converted to digital data. 
         [0054]    Data coming from the terminal section  501  passes through the interface section  408  to reach the baseband processing section  407  for OFDM modulation and D/A conversion. The processing by the baseband processing section  407  turns the data into a PLC signal that is sent to the transmission section  406  for amplification. The PLC signal amplified by the transmission section  406  is forwarded through the coupling section  404  to the coil  206 . The coil  206  transmits the PLC signal in the form of electromagnetic waves to the coil  204  of the electromagnetic coupling sheet  202 . 
         [0055]    The baseband processing section  407 , as mentioned above, further performs MAC processes including framing, de-framing, error correction, and retransmission. The communication status display section  503  is provided to inform the user of ongoing communication status using different color indications and blinking frequencies in a manner reflecting the level of reception, the number of successfully received packets, and other conditions. 
         [0056]      FIG. 5  schematically depicts typical steps to be taken by PLC modems for communication. In the communication procedure of  FIG. 5 , the master-slave relationships are assumed to be established among the PLC modems. Specifically, it is assumed that the PLC modem  1  acts as the master and that the PLC modems  2  and  3  serve as slaves, each of the latter being representative of the PDA  205 . 
         [0057]    The PLC modem  1  transmits beacon signals  600  intermittently. Although not shown in  FIG. 5 , the PLC modem  1  keeps sending out the beacon signal throughout the ensuing communication. 
         [0058]    Upon receipt of a beacon signal, the PLC modem  2  returns an entry signal  601  to the PLC modem  1 . The PLC modem  1  in turn sends an enable signal  602  which is received by the PLC modem  2 . The PLC modem  3  performs the same slave sequence as that of the PLC modem  2  as indicated by reference numerals  603  and  604 . 
         [0059]    With the above sequences completed, communication can take place at any time between the configured modems on a connectionless basis. That is, the PLC modems  1 ,  2  and  3  can communicate with one another on a carrier sense multiple access with collision avoidance (CSMA/CA) network  605 . 
         [0060]    It should be noted that the PLC modems  2  and  3  serving as slaves must keep on receiving the beacon signals from the PLC modem  1  acting as the master. 
         [0061]    In the communication procedure shown in  FIG. 5 , data is transmitted on a best-effort basis. For applications such as streaming schemes that require high quality of service (QoS), data communication intervals are placed under concentrated control of the PLC modem  1  acting as the master. 
         [0062]    In the foregoing description, the PDA  205  equipped with a PLC modem and a coil for electromagnetic coupling was shown to participate in the PLC network through the intervention of the coupling device such as the dedicated electromagnetic coupling sheet  202 . However, unlike ordinary wired communication networks that utilize coaxial cables resistant to signal leakage, the PLC setup entails some signals leaking from a number of spots along the power line. The inventors of the present application think it possible to take advantage of such leakage signals from the power line within the framework of signal transmission and reception by use of the electromagnetic coupling effect occurring between the coil and the power line. The PDA  205  can thus take part in the PLC network for communication using such leakage signals. 
         [0063]      FIG. 6  is a schematic view showing a typical setup where the PDA  205  conducts communication using leakage power from the power line without recourse to the dedicated electromagnetic coupling sheet  202 . In  FIG. 6 , reference numeral  700  stands for a power strip;  701  for an outlet part of the power strip;  702  for a cable part of the power strip; and 703 for a wall outlet. A PLC signal leaks from those parts designated by reference numerals  701  through  703 . Bringing the PDA  205  close to or in contact with any one of such signal-leaking parts allows the device to conduct PLC-based data exchanges. 
         [0064]    The leakage power from the parts above is at lower levels than that from the dedicated electromagnetic coupling sheet  202 . That means throughput can be reduced correspondingly. Still, in the inventors&#39; view, the method of communication illustrated in  FIG. 6  can bring about significant advantages given that the dedicated sheet is not needed. 
         [0065]      FIG. 7  schematically shows how mobile devices communicate with each other without the intervention of power line communication channels. Two PDAs (PDA  205 , PDA  800 ) placed on the electromagnetic coupling sheet  202  communicate with each other using their respective electromagnetic connections to the coupling sheet  202 . 
         [0066]    There are cases where two PDAs acting as two slaves can communicate with each other without the need for beacon signals from the master PLC modem  103 . In such cases, the electromagnetic coupling sheet  202  is not needed; the two PDAs need only be brought close to each other. 
         [0067]    Although the description above contains many specificities, these should not be construed as limiting the scope of the present application but as merely providing illustrations of some of the presently preferred embodiments of this present application. It is to be understood that changes and variations may be made by those skilled in the art without departing from the spirit or scope of the claims that follow. 
         [0068]    The foregoing description described the mobile device and the electromagnetic coupling sheet to be connected with one another through a magnetic field occurring therebetween. However, an electric field is also considered to play a significant role in the connection. Thus the present application is not limited by the effect of electromagnetic coupling. 
         [0069]    It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.