Communication repeater and communication system

A communication repeater comprises a transmitting and receiving that performs wireless communication with a communication device, a power-line carrier communication unit that performs power-line carrier communication with the communication device, and a control unit. The control unit selects either one of the wireless communication and the power-line carrier communication according to conditions.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2010-076294, filed on Mar. 29, 2010. The content of which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication repeater that wirelessly transmits and receives a communication signal.

2. Description of the Related Art

A mobile communication device such as a mobile phone and Personal Handy-phone System (PHS) performs communication with other communication devices by receiving a communication signal output from a base station directly or via a communication repeater. As for a method of communication performed by a mobile communication device, performing communication with power-line carrier communication is proposed (see, for example, Japanese Patent Application Publication Laid-Open No. 2003-169004).

The communication repeater can perform communication with communication devices within a certain area by wirelessly transmitting and receiving a communication signal. However, even if the physical distance is close, there may be areas with which the communication repeater cannot perform communication, for example, the underground of a building where there are many objects (such as walls and floors) that block or attenuate a communication wave.

Japanese Patent Application Publication Laid-Open No. 2003-169004 describes how a mobile communication device performs power-line carrier communication by using a charging stand, but fails to describe any apparatus that is caused to transmit a communication signal of the power-line carrier communication. Moreover, a communication signal superimposed on a power line cannot maintain its signal components after passing through a substation directly. Thus, it becomes necessary to install facilities such as providing equipment to bypass a communication signal for each substation to ensure communication in a wider area with power-line carrier communication.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a communication repeater, having: a transmitting and receiving unit that transmits and receives a communication signal to/from a communication device with wireless communication; a power supply unit connected to a power line; a power-line carrier communication unit that transmits and receives a communication signal superimposed on a carrier transmitted over the power line from/to the communication device; and a control unit that controls wireless communication of the transmitting and receiving unit with the communication device and power-line carrier communication of the power-line carrier communication unit with the communication device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail below with reference to drawings. The present invention is not restricted the following description. Elements in the description that follows contain elements a person skilled in the art can easily assume or substantially the same elements, that is, elements in the scope of so-called equivalents.

FIG. 1is a schematic block diagram of an example of a communication system having a communication repeater according to an embodiment of the present invention. A communication system10includes a base station12, communication repeaters (hereinafter, called “repeaters”)14and16, a power line18, a commercial power supply19, power converters20,20a, and20b, and mobile communication devices22,22a, and22b. WhileFIG. 1illustrates only one base station12and the repeaters14and16, a host of the base stations12and the repeaters14and16may be arranged in a communication network. Also, a host of the power converters20,20a, and20b, and the mobile communication devices22,22a, and22bmay be arranged.

The base station12is a communication apparatus that wirelessly transmits and receives a communication signal to/from the mobile communication devices22,22a, and22band the repeaters14and16. The base station12is also connected to the other base stations12(not illustrated) by wire or by wireless medium and transmits and receives a communication signal to/from the other base stations12. The communication system10forms a communication network by transmitting and receiving a communication signal among base stations. The communication signal is a signal of data transmitted or received for a phone call, mail, or Internet communication.

The base station12can also communicate with (transmit and receive a communication signal to/from) other communication device apparatuses in another communication network, for example, in a communication network of another carrier by connecting a portion of the communication network including the base station12to an exchange.

The repeaters14and16are wireless relay stations that wirelessly transmit and receive a communication signal to/from the corresponding base station12. The repeater14and the repeater16have the same configuration with only a difference of installation location. Thus, hereinafter, the repeater14will representatively be described.FIG. 2is a schematic block diagram of the communication repeater illustrated inFIG. 1.

The repeater14is a communication apparatus capable of transmitting and receiving a communication signal with wireless communication and transmitting and receiving a communication signal with power-line carrier communication. The repeater14includes, as illustrated inFIG. 2, a wireless communication unit30, an antenna31, a modem (modulator and demodulator)32, a power transformer34, an external power supply device (power supply unit)36, a state determination unit38, and a control unit40.

The power-line carrier communication is also called Power Line Communication (PLC), Power Line Telecommunication (PLT), or power line communication. The power-line carrier communication is a technology to use power wiring installed in homes or offices as communication lines of full duplex communication having a bus network configuration. In the power-line carrier communication, a modulation method such as the orthogonal frequency domain multiplex (OFDM) using fast Fourier transforms or wavelet transforms, the spread spectrum (SS) techique capable of alleviating the reduction in speed due to an influence of noise, or the discrete multi-frequency (DMT method) can be adopted.

The wireless communication unit30performs wireless communication with the base station12, the wireless communication unit of another repeater, or a mobile communication device via the antenna31. The wireless communication unit30enables communication between the base station12and a mobile communication device by transmitting a communication signal transmitted from the base station12to the mobile communication device and transmitting a communication signal transmitted from the mobile communication device to the base station12. That is, the wireless communication unit30and the antenna31wireless relay communication signals transmitted between the base station12and the mobile communication device. The wireless communication unit30performs, for example, wireless communication by time-division multiplexing or the like. The wireless communication by time-division multiplexing performs communication by obtaining a plurality of time slots by time division of a frame in the base station12and by assigning each of the slots obtained to a channel of the mobile communication device or the like. The wireless communication unit30also relays communication signals transmitted between the base station12and the wireless communication unit of another repeater via the antenna31wirelessly.

The wireless communication unit30further transmits a communication signal transmitted from the base station12or the wireless communication unit of another repeater and received with wireless communication via the antenna31to the modem32. The wireless communication unit30transmits a communication signal transmitted from the modem32to the base station12or the wireless communication unit of another repeater with wireless communication via the antenna31.

The modem32is a modulator-demodulator that converts the communication method of a communication signal. The modem32modulates a communication signal transmitted from the wireless communication unit30into a communication signal used for power-line carrier communication. Then the modem32transmits the modulated communication signal to the power line18(power-line carrier communication network) from the power transformer34. The model32also demodulates a communication signal superimposed onto a carrier of power (power waveform) fed to the power transformer34via the external power supply device36from the power line18(power-line carrier communication network) into a communication signal used for wireless communication.

The power transformer (power-line carrier communication unit)34is connected to the power line18installed in homes or offices via the external power supply device36. The power transformer34receives power fed from the commercial power supply19(described later) connected to the power line18, and transforms the received power into power that can be used by the repeater14. The power transformer34feeds the transformed power to each unit via the control unit40. The power transformer34also transmits a communication signal superimposed on a power waveform of the power line18to the modem32. The power transformer34superimposes a communication signal transmitted from the modem32on a power waveform and supplies the superimposed communication signal to the power line18.

The external power supply device36is a device connected to the power line18. The external power supply device36is, for example, an outlet.

The state determination unit38includes a communication quality detection unit42that detects a communication quality value indicating quality of a communication signal and a traffic detection unit44that detects a traffic (communication traffic) amount of a communication signal. More specifically, the state determination unit38measures quality of communication with wireless communication and quality of communication with power-line carrier communication through the communication quality detection unit42. The communication quality detection unit42determines communication quality of a measurement target based on, for example, the Received Signal Strength Indicator (RSSI) indicating the signal strength, the minimum data transfer rate Committed Information Rate (CIR) guaranteed for each fixed connection party by the frame relay, the Carrier to Interference and Noise Ratio (CINR) indicating a carrier power to interference and noise power ratio, the signal power value, the signal power value by High Pass Filter (HPF) or Band Pass Filter (BPF), or the communication speed. The state determination unit38also measures the amount of traffic in each communication based on the number of lines or the amount of communication signal processed by the modem32and the wireless communication unit30through the traffic detection unit44.

The control unit40comprises a semiconductor integrated circuit including a central processing unit (CPU) and a storage unit in which data and programs necessary for processing are stored. The control unit40manages and controls the whole repeater14based on programs and data stored in the storage unit and states of the state determination unit38, the wireless communication unit30, and the modem32.

The repeater14is configured as described above and uses the wireless communication unit30to transmit and receive a communication signal to/from the base station12, the wireless communication unit of another repeater, or a mobile communication device with wireless communication. The repeater14also uses the modem32and the power transformer34to transmit and receive a communication signal via the power line18with power-line carrier communication.

Returning toFIG. 1, the description of the communication system10will continue. The power line18is a path to transfer power. The power line18is connected to the repeater14or an external power supply device (outlet) provided in buildings, offices, and homes. The power line18feeds power fed from the commercial power supply19to each device via the external power supply device. The power line18transmits a carrier on which a communication signal superimposed.

The commercial power supply19is a transformation unit, that is, an apparatus that feeds power generated by a power station or the like to the power line18. The commercial power supply19feeds power to the power line18.

The power converters20,20a, and20bare devices connected to the power line18. The power converters20,20a, and20bhave a function similar to that of the modem32and the power transformer34of the repeater14. The power converters20,20a, and20bhave the common basic configuration. Thus, hereinafter, the power converter20will representatively be described. The power converter20converts a carrier-superimposed communication signal supplied from the power line18into a communication signal that can be received by a mobile communication device and transmits the converted communication signal to the mobile communication device. The method of transmitting a communication signal from the power converter20to the mobile communication device is not particularly limited. The power converter20also converts a communication signal transmitted from the mobile communication device into a communication signal used for power-line carrier communication. The power converter20may include a function to charge the mobile communication device by feeding power to the mobile communication device fed from the power line18.

Communication between the power converters20,20a, and20band the mobile communication devices22,22a, and22bwill be described below. The power converter20ahas an antenna. The power converter20atransmits and receives a communication signal to/from the mobile communication device22awith wireless communication. In this case, the power converter20aconverts a carrier-superimposed communication signal supplied from the power line18into a communication signal of wireless communication. As for a method of wireless communication, for example, a method similar to the method of wireless communication performed between the base station12and the mobile communication device may be used. In this case, the mobile communication device can perform communication by using the function to perform communication with the base station12. The power converter may also perform wireless communication through infra-red communication or short-distance communication such as Bluetooth.

The power converter20bis connected to the mobile communication device22bvia a power line. The power converter20btransmits and receives a communication signal to/from the mobile communication device22bwith wire communication. In this case, the power converter20bmay also perform communication with power-line carrier communication or may perform communication with a dedicated wire communication line.

The mobile communication devices22,22a, and22bare devices that transmit and receive a communication signal to/from the base station12through various paths described above. The mobile communication devices22,22a, and22bconverts a received communication signal into a voice, character string, or image for output to a receiver, speaker, display unit or the line. The mobile communication devices22,22a, and22balso convert an input voice, character information, or image into a communication signal for output to the base station12. The mobile communication device22,22a, and22benables a phone call, a mail communication, or an access for a Web site by transmitting and receiving a communication signal to/from other communication devices via the base station12, the repeaters14and16or the like. As the mobile communication device, a mobile phone, Personal Handy-phone System (PHS), PDA, portable navigation apparatus, portable game machine or the like can be used.

Next, communication paths of the communication system10will be described usingFIG. 3.FIG. 3is a diagram for explaining communication paths of the communication system illustrated inFIG. 1. As illustrated inFIG. 3, the communication system10can connect the base station12and the mobile communication device22by four communication paths. That is, the communication system10can put the base station12and the mobile communication device22into a state ready to transmit and receive a communication signal by four communication paths.

The communication system10has, as a first path, a path to transmit and receive a communication signal between the base station12and the mobile communication device22on which the base station12and the repeater14perform communication with wireless communication60, the repeater14and the power converter20perform communication with power-line carrier communication62, and further the power converter20and the mobile communication device22perform communication with power-line carrier communication64. The communication system10has, as a second path, a path to transmit and receive a communication signal between the base station12and the mobile communication device22on which the base station12and the repeater14perform communication with the wireless communication60, the repeater14and the power converter20perform communication with the power-line carrier communication62, and further the power converter20and the mobile communication device22perform communication with wireless communication66. The communication system10has, as a third path, a path to transmit and receive a communication signal between the base station12and the mobile communication device22on which the base station12and the repeater14perform communication with the wireless communication60and the repeater14and the mobile communication device22perform communication with wireless communication68. The communication system10has, as a fourth path, a path to transmit and receive a communication signal between the base station12and the mobile communication device22on which the base station12and the mobile communication device22perform communication with wireless communication70.

The communication system10can also connect the repeater14and the repeater16by two communication paths. That is, the communication system10can put the repeater14and the repeater16into a state ready to transmit and receive a communication signal by two communication paths. More specifically, the communication system10has a path on which the repeater14and the repeater16transmit and receive a communication signal by performing wireless communication72between the repeater14and the repeater16. The communication system10has another path on which the repeater14and the repeater16transmit and receive a communication signal by performing power-line carrier communication74between the repeater14and the repeater16.

By providing the repeater14capable of communicating with the mobile communication device22with the power-line carrier communication62, as illustrated inFIG. 4, the communication system10enables communication between the repeater14and the mobile communication device22without using the wireless communication.FIG. 4is a diagram for explaining the operation of the communication system. By providing the repeater14outside a building80and the power converter20, which is an output unit for power-line carrier communication, inside the building80, like the communication system10illustrated inFIG. 4, communication can be performed from an area inside the building80where a wireless wave of the repeater14is not received (such as the underground of the building and inside a room with a thick wall (steel frame)).

Moreover, the power line18already wired inside the building80is used and thus, a communication signal can be transmitted without newly providing a line. Thus, by providing the repeater14, the communication system10can cause a communication signal to reach a wider area. Also, the power line18can be used and therefore, a constitution of the communication system10can be applied to various objects having an outlet. By installing the repeater14in, for example, a vehicle such as an electric train or automobile, a user riding in the vehicle can transmit and receive a communication signal via an outlet. Thus, by performing communication via the fixed repeater14, a mobile communication device can perform communication without searching and switching a base station for communication. The repeater14communicates with the base station12wirelessly, and the repeater14has a higher functionality of transmitting and receiving a communication signal than a mobile communication device. Thus, the repeater14improves the quality of the communication system10as a whole.

If a system is configured in such a way a power line passes with a substation or the like, it becomes necessary for power-line carrier communication to temporarily extract the communication signal for voltage transformation and then to superimpose the communication signal again. However, if a system configured in such a way a communication signal is transmitted and received with a repeater, a power line inside a building where the repeater is installed and the like, the power line does not generally pass with a substation and thus, a communication signal can be transmitted and received appropriately. While there is a certain limit of power-line carrier communication to the amount of signal that can be superimposed on a power line (the number of lines by which communication is performed), the power line can be used more effectively by making a conversion for each of the repeaters14and16. That is, by performing power-line carrier communication for each of the repeaters14, power-line carrier communication can be performed for each area centered on each of the repeaters14. Accordingly, the same wavelength can be used for different areas and therefore, power-line carrier communication can be performed by the more number of lines.

The communication system10can connect the base station12and the mobile communication device22described above with four paths and therefore, with the increased choice, a more suitable communication state can be realized in a wider range.

By performing power-line carrier communication together with the repeater16, the repeater14can select the communication method in accordance with intended use. Moreover, communication can be performed by using both wireless communication and power-line carrier communication and therefore, the amount of communication signal transmitted/received at a time can be increased.

The repeater14can communicate with the mobile communication device22through both the wireless communication68and the power-line carrier communication62and therefore, the repeater14can select the communication method to be used. Accordingly, the repeater14can communicate with the mobile communication device using a more appropriate communication method. An example of selecting the communication method by the repeater14will be described below usingFIG. 5.FIG. 5is a flow chart illustrating the operation of the communication system.

First, in step S12, the repeater14starts communication with the device (the mobile communication device22). The repeater14starts communication with the mobile communication device22when the repeater14detects an incoming signal from another communication device to the mobile communication device22, that is, transmission of a signal making a notification of voice communication, mail or the like from the base station12. The repeater14also starts communication with the mobile communication device22when the repeater14detects an outgoing signal from the mobile communication device22to another communication device, that is, transmission of a signal making a notification of voice communication, mail or the like from the mobile communication device22. The repeater14detects the mobile communication device22with which the repeater14can communicate at predetermined intervals. When communication is started, the repeater14starts communication with the pre-detected mobile communication device22. By detecting the mobile communication device22with which the repeater14can communicate in advance, the repeater14can determine, when an incoming signal is received from another communication device via the base station12, whether the mobile communication device to be communicated is the mobile communication device22with which the repeater14can communicate.

After starting communication in step S12, in step S14, the repeater14performs communication by the PLC method (power-line carrier communication). That is, the repeater14uses the PLC method as the communication method when the communication is started.

After setting the PLC method as the communication method in step S14, in step S16, the repeater14determines whether PLC communication quality<wireless communication quality holds. The PLC communication quality is quality of communication with power-line carrier communication, that is, quality of communication performed with the mobile communication device22with power-line carrier communication by using the modem32and the power transformer34. The PLC communication quality can be determined by the communication quality detection unit42of the state determination unit38. The wireless communication quality is quality of communication performed with the mobile communication device22with wireless communication by using the wireless communication unit30. The wireless communication quality can be determined based on the state determination unit38. The state determination unit38may determine quality by analyzing a communication signal used actually for communication (that is, a communication signal transmitted and received between the mobile communication device22and another communication device). The state determination unit38may determine quality by transmitting and receiving a communication signal created for quality determination on each path between the repeater14and the mobile communication device22and analyzing results thereof. The state determination unit38may also detect quality of two communication methods by performing communication of the two communication methods simultaneously or by temporarily switching to communication by the wireless method while performing communication by the PLC method.

If the repeater14determines in step S16that PLC communication quality<wireless communication quality does not hold (No), that is, PLC communication quality≧wireless communication quality holds, in step S18, the repeater14determines whether to terminate the processing. That is, in step S18, the repeater14determines whether to terminate communication with the mobile communication device22with which communication is being performed. If the repeater14determines in step S18that communication with the mobile communication device22should not be terminated (No), that is, communication with the mobile communication device22should be continued, the repeater14proceeds to step S14. If the repeater14determines in step S18that communication with the mobile communication device22should be terminated (Yes), the repeater14proceeds to step S28. Thus, if PLC communication quality is maintained higher than wireless communication quality, the repeater14performs communication with the mobile communication device22with PLC communication until communication is terminated.

If the repeater14determines in step S16that PLC communication quality<wireless communication quality holds (Yes), in step S20, the repeater14determines whether PLC communication traffic≦threshold holds, that is, PLC communication traffic is equal to the threshold or less. The PLC communication traffic can be determined by the traffic detection unit44of the state determination unit38. If the repeater14determines in step S20that PLC communication traffic≦threshold holds (Yes), the repeater14proceeds to step S14. That is, if the repeater14determines that the PLC communication traffic is equal to the threshold or less, the repeater14continues communication by the PLC method.

If the repeater14determines in step S20that PLC communication traffic>threshold holds (No), in step S22, the repeater14performs communication by the wireless method. That is, if the repeater14determines that the PLC communication traffic is higher than the threshold (PLC communication lines are congested or the amount to be processed is large), the repeater14switches communication with the mobile communication device22from the PLC method to the wireless method.

After switching the communication method to the wireless method (wireless communication) in step S22, in step S24, the repeater14determines whether traffic has decreased. Various settings can be used as criteria for determining whether traffic has decreased. For example, traffic may be determined to have decreased if traffic becomes equal to the threshold used in step S20or less or traffic may be determined to have decreased if traffic decreases by a fixed amount or more.

If the repeater14determines in step S24that traffic has decreased (Yes), the repeater14proceeds to step S14to repeat the above processing. Accordingly, when traffic has decreased by the fixed amount or more, the repeater14re-selects the PLC method or the wireless method as the communication method.

If the repeater14determines in step S24that traffic has not decreased (No), in step S26, the repeater14determines whether to terminate communication. If the repeater14determines in step S26that communication with the mobile communication device22should not be terminated (No), that is, communication with the mobile communication device22should be continued, the repeater14proceeds to step S24. If the repeater14determines in step S26that communication with the mobile communication device22should be terminated (Yes), the repeater14proceeds to step S28.

If the repeater14determines in step S18or S26that communication with the mobile communication device22should be terminated (Yes), in step S28, the repeater14performs termination processing, more specifically, processing to terminate communication with the mobile communication device22. Then, the repeater14terminates the present processing.

Thus, by acquiring quality of PLC communication performed with the mobile communication device22and quality of wireless communication with the state determination unit38and selecting the communication method to be used based on the comparison result, the repeater14can perform communication in higher quality. That is, the repeater14can select the communication method which provides a better communication state.

As illustrated inFIG. 5, by making determinations based on traffic of PLC communication, the communication state can be determined without analyzing communication quality each time. Accordingly, the load of processing performed by the repeater14can be reduced.

In the above embodiment, the communication method to be used for communication is selected based on communication quality and traffic, but may be selected based on one of communication quality and traffic.

In the above embodiment, the communication method to be used for communication is selected based on communication quality and traffic, but the present invention is not limited to this. The repeater14can select the communication method with the mobile communication device22by various methods.

For example, the repeater14may be set to perform power-line carrier communication with only preset mobile communication devices (mobile communication devices having individual preset identification number). That is, the repeater14may communicate with unregistered mobile communication devices with only wireless communication, though these mobile communication devices are communicable with power-line carrier communication. Thus, by adopting a setting to enable only registered mobile communication devices to perform power-line carrier communication with the repeater14, the power-line carrier communication can be made available to specific target users. Accordingly, for example, the power-line carrier communication can be made available to only persons involved in a building where the repeater14is installed so that the power-line carrier communication whose number of lines is limited can be used satisfactorily. Moreover, the repeater14converts only specific target communication into power-line carrier communication and thus, the load of information processing can be reduced.

It is preferable for the repeater14to set priorities to mobile communication devices so that mobile communication devices with higher priorities preferentially use power-line carrier communication. By making such priorities settable, power-line carrier communication can be used more effectively.

The repeater14in the above embodiment relays communication between the base station12and the mobile communication device22, that is, communication signals transmitted between the mobile communication device22and other communication devices via the base station12, but the present invention is not limited to this. In addition to the relay of communication signals between the base station12and other communication devices, the repeater14may relay communication signals that do not go with the base station12. That is, the repeater14may relay communication signals transmitted between two mobile communication devices that can communicate with the same repeater14. In other words, the repeater14may have a function as a base station of internal network within an area where the repeater14can communicate.

The repeater14may also transmit and receive communication signals from/to a mobile communication device that can communicate with the repeater14and a mobile communication device that can communicate with the other repeater14connected to power-line carrier communication without going through the base station12. That is, a network, for example, a Virtual Private Network (VPN) may be formed by a plurality of the repeaters14. In this case, the danger of wireless transmission being intercepted and information being acquired can be reduced by performing communication with power-line carrier communication.

In the above embodiment, the power converter20and the mobile communication device22are presented as separate devices, but the power converter20and the mobile communication device22may be integrated. The power converter20may have only the charging function mounted thereon to mount the modem function on the mobile communication device22. Or, the power converter20may only have the function for transmitting and receiving communication signals without having the charging function.

A communication repeater according to the present invention achieves an effect of being able to enable communication with an area where communication cannot be performed with the outer area with wireless communication or quality of wireless communication deteriorates and to transmit and receive a communication signal to/from communication devices appropriately.