Power line communication device and power line communication method

Abstract

To provide a power line communication device capable of performing appropriate communication when performing power line communication using a power line of a DC power supply in a mobile body.SOLUTION: A power line communication device 10 for performing power line communication using a power line 2 of a DC power supply (battery) 3 in a mobile body includes: a communication unit 11 that performs power line communication using the DC power line 2; an identification unit 12 that identifies a frequency band with less attenuation than other frequency bands among a plurality of frequency bands used in power line communication; and a communication control unit 13 that controls the communication unit 11 so as to perform power line communication using the identified frequency band. The identification unit 12 repeatedly identifies a frequency band with less attenuation than other frequency bands.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power line communication device or the like that performs power line communication using a power line of a DC power supply. [Background technology]

[0002] As the functionality of automobiles and other mobile objects becomes more advanced, the amount of wiring inside them increases. This increases the weight of the entire mobile object, and this leads to a decrease in fuel efficiency (electricity efficiency in the case of electrically powered vehicles). One way to avoid this is to use battery lines (power lines) to transmit control information, etc.

[0003] For example, the number of wire harnesses is reduced by performing power line communication using the battery line of an automobile (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-193799 Summary of the Invention [Problem to be solved by the invention]

[0005] In the power line communication system described in Patent Document 1, in order to reduce the influence on power line communication of noise generated when the motor in the electrical equipment mounted on the automobile is driven, a frequency band with a low noise level generated by the electrical equipment is selected, and power line communication is carried out in that frequency band.

[0006] However, power line communications in mobile vehicles such as automobiles are not only affected by the electrical equipment installed on the vehicle. Battery lines, which are primarily used to supply DC power, have the characteristic of being difficult for high-frequency signals to pass through. Power line communications are also affected by, for example, the wiring conditions, length, thickness, and curvature of the power lines between the communicating devices. Such wiring conditions vary depending on the type of mobile vehicle and may also vary from one mobile vehicle to another. Furthermore, noise and interference waves from the surrounding area of ​​the mobile vehicle can interfere with power line communications via the battery line. In this case, transmission characteristics can change depending on the time of day and the current location of the mobile vehicle.

[0007] In this way, even if a frequency band has a low noise level from electrical equipment, the transmission characteristics may not be good depending on the wiring conditions, etc., and the transmission characteristics may also be poor depending on the time of day or the current location of the mobile object.

[0008] The present invention has been made to solve the above-mentioned problems, and has an object to provide a power line communication device or the like that can realize appropriate communication when performing power line communication using a power line of a DC power supply in a mobile object. [Means for solving the problem]

[0009] In order to achieve the above object, a power line communication device according to one aspect of the present invention is a power line communication device that performs power line communication using a power line of a DC power source in a mobile body, and includes: a communication unit that performs power line communication using the DC power line; an identification unit that identifies a frequency band that has less attenuation than other frequency bands from among multiple frequency bands used in power line communication; and a communication control unit that controls the communication unit to perform power line communication using the identified frequency band. This configuration enables power line communication to be performed using a frequency band with less attenuation via the power line of a DC power supply in a mobile object, which, for example, enables power line communication with fewer errors and improves the quality of power line communication between devices.

[0010] In the power line communication device according to an aspect of the present invention, the identifying unit may repeatedly identify a frequency band that has less attenuation than other frequency bands. With this configuration, it becomes possible to realize power line communication using a suitable frequency band in accordance with changes over time and changes depending on location of interference radio waves and the like.

[0011] In the power line communications device according to an aspect of the present invention, the identifying unit may acquire transmission characteristics for each frequency band and identify a frequency band with less attenuation than other frequency bands using the transmission characteristics. In the power line communication device according to an aspect of the present invention, the transmission characteristics may be a packet error rate, a packet acquisition rate, or an attenuation characteristic. In the power line communications device according to an aspect of the present invention, the identifying unit may acquire a frequency band that is included in a signal transmitted from another power line communications device and that has less attenuation than other frequency bands.

[0012] The power line communication device according to an aspect of the present invention may further include an impedance matching unit that performs impedance matching between the communication unit and the DC power line. With this configuration, it is possible to match the impedance between the communication unit and the power line, and it becomes possible to transmit signals efficiently over the power line.

[0013] Furthermore, a power line communication method according to one aspect of the present invention is a power line communication method for performing power line communication using a power line of a DC power supply in a mobile body, and includes the steps of identifying a frequency band from among a plurality of frequency bands used in the power line communication, which has less attenuation than other frequency bands, and performing power line communication using a DC power line using the identified frequency band. [Effects of the Invention]

[0014] According to a power line communication device or the like according to one aspect of the present invention, power line communication is performed in a mobile object via a power line of a DC power supply using a frequency band that has less attenuation than other frequency bands, thereby enabling higher quality communication to be achieved. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram showing the configuration of a power line communication system according to an embodiment of the present invention. [Figure 2] A flowchart showing the operation of the power line communication device according to the embodiment. [Figure 3] FIG. 2 shows an example of the arrangement of devices in a moving body according to the embodiment. [Figure 4] FIG. 2 shows an example of the arrangement of devices in a moving body according to the embodiment. [Figure 5A] FIG. 10 is a diagram showing an example of measured values ​​of transmission characteristics for each frequency in the embodiment; [Figure 5B] FIG. 10 is a diagram showing an example of measured values ​​of transmission characteristics for each frequency in the embodiment; [Figure 6A] FIG. 10 is a diagram showing an example of transmission characteristics for each frequency in the embodiment; [Figure 6B] FIG. 10 is a diagram showing an example of transmission characteristics for each frequency in the embodiment; [Figure 7] FIG. 2 is a diagram showing an example of a connection between a communication unit and a power line according to the embodiment; [Figure 8] FIG. 2 is a diagram showing an example of a connection between a communication unit and a power line according to the embodiment; [Figure 9] FIG. 10 is a diagram showing another example of the communication unit in the embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0016] A power line communication device and a power line communication method according to the present invention will be described below using embodiments. In the following embodiments, components and steps denoted by the same reference numerals are the same or equivalent, and repeated description may be omitted. The power line communication device according to this embodiment identifies a frequency band with little attenuation in power line communication (PLC) via a power line of a DC power supply in a mobile object, and performs power line communication using the identified frequency band.

[0017] 1 is a block diagram showing the configuration of a power line communication system 100 according to this embodiment. Power line communication system 100 according to this embodiment includes master device 1-1 and slave devices 1-2 to 1-N that perform power line communication via a power line (battery line) 2 connected to a battery 3, which is a DC power source in a mobile object. Here, N is an integer equal to or greater than 2. Note that master device 1-1 may be considered to be a base station, and the other slave devices 1-2 to 1-N may be considered to be terminal stations.

[0018] The mobile body is not particularly limited as long as it has a power line of a DC power source, and may be, for example, an automobile, a ship, an airplane, a train, or any other mobile body having a power line of a DC power source. In this embodiment, a case where the mobile body is an automobile will be mainly described. In an automobile, for example, power is supplied using a single power line (wiring) 2 with the chassis as the ground, and therefore power line communication is also performed using the chassis ground and the single power line 2. Furthermore, the wiring of the power line 2 is complex and the transmission characteristics vary greatly depending on the location, but in the power line communication system 100 according to this embodiment, power line communication is performed by switching frequencies according to the transmission characteristics.

[0019] The power from the DC power source supplied via the power line may be used, for example, to drive a vehicle such as an electric vehicle for transportation, or may be used to operate electrical equipment in the vehicle, such as a navigation system, audio equipment, or a motor for opening and closing windows.

[0020] Master device 1-1 includes power line communications device 10-1 and a reception unit 20-1. Master device 1-1 transmits information (such as control information) corresponding to an operation received by reception unit 20-1 to slave devices 1-2 to 1-N. Each component included in master device 1-1, such as power line communications device 10-1 and reception unit 20-1, normally operates using power supplied from battery 3 via power line 2.

[0021] The slave device 1-2 includes a power line communication device 10-2 and an electric device 20-2. The slave device 1-2 operates the electric device 20-2 using information received from the master device 1-1 by the power line communication device 10-2. The electric device 20-2 may be, for example, an audio system, a navigation system, a motor for opening and closing a window, a motor for opening and closing a door mirror, a motor for driving a wiper, or a motor for driving an air conditioning fan. Each component included in the slave device 1-2, such as the power line communication device 10-2 and the electric device 20-2, typically operates using power supplied from a battery 3 via a power line 2. The slave devices 1-3 to 1-N have the same configuration as the slave device 1-2, and detailed description thereof will be omitted. For example, the slave devices 1-3 to 1-N may include power line communication devices 10-3 to 10-N and electric devices 20-3 to 20-N, respectively. Furthermore, for example, power line communications devices 10-3 to 10-N may include communications units 11-3 to 11-N, identification units 12-3 to 12-N, communication control units 13-3 to 13-N, and control units 14-3 to 14-N, respectively.

[0022] When there is no need to distinguish between the power line communication devices 10-1, 10-2, etc., they may be referred to as the power line communication device 10. The same applies to other components, such as the communication units 11-1 and 11-2 and the identification units 12-1 and 12-2.

[0023] 3 and 4 are diagrams showing an example of the connection status via power lines 2 between a master device 1-1, slave devices 1-2 to 1-5, and a battery 3 in a moving object 4, which is an automobile. As shown in FIGS. 3 and 4, when the connection status of each device in the moving object 4 differs, the transmission characteristics between the devices will change. For example, the transmission characteristics between the master device 1-1 and slave device 1-3 in FIG. 3 may differ from the transmission characteristics between the master device 1-1 and slave device 1-3 in FIG. 4. Therefore, it is necessary to measure the transmission characteristics between the devices. Furthermore, the transmission characteristics may change over time. This is because the surrounding interference radio wave conditions change as the moving object 4 moves. Therefore, it is preferable to repeatedly measure the transmission characteristics between the devices.

[0024] The communication unit 11 performs power line communication using a DC power line 2. The communication unit 11 may have, for example, a communication device for performing power line communication. The frequency used in power line communication is not particularly limited, but may be, for example, a frequency in the range of 10 kHz to 150 MHz, or other frequencies. Note that power line communication is already known, and a detailed description thereof will be omitted.

[0025] The identifying unit 12 identifies a frequency band with less attenuation than other frequency bands from among multiple frequency bands used in power line communication. The frequency band with less attenuation may be, for example, a frequency band that can achieve higher-quality transmission. The frequency band with less attenuation than other frequency bands may be, for example, the frequency band with the least attenuation, or the frequency band with the second least attenuation. In the latter case, the frequency band with less attenuation than other frequency bands may be, for example, a frequency band selected from multiple frequency bands with less attenuation, excluding a frequency band known to have a lot of interference. Here, the interfering radio waves may change depending on the movement of the mobile object on which the power line communication device 10 is installed or over time, and as a result, the frequency with less attenuation may change. Therefore, it is preferable that the identifying unit 12 repeatedly identifies a frequency band with less attenuation than other frequency bands, as described above. The identifying unit 12 may, for example, periodically repeat the identification of a frequency band with less attenuation. In this case, for example, the frequency band used in power line communication is adaptively switched using the identification result. Furthermore, the identification unit 12 may repeat the identification of a frequency band with less attenuation for each predetermined moving distance of the moving object, for example.

[0026] Furthermore, the identifying unit 12 may identify a frequency band with less attenuation than other frequency bands, for example, when power line communication in the power line communication system 100 is started, for example, when the power line communication system 100 is started. Furthermore, if the wiring situation regarding the power line 2 in the mobile object changes, for example, if a new device is connected to the power line 2, the transmission characteristics may change. In such a case, the identifying unit 12 may also identify a frequency band with less attenuation than other frequency bands, for example.

[0027] The degree of attenuation can be known from transmission characteristics. The transmission characteristics may be, for example, transmission quality. The transmission characteristics are not particularly limited and may be, for example, a packet error rate, a packet acquisition rate, or attenuation characteristics. The packet acquisition rate is a value indicating the ratio of the number of received packets to the number of transmitted packets. The attenuation characteristics are information indicating the degree of attenuation of a received signal relative to the transmitted signal. If the strength of a transmitted signal is constant, the attenuation characteristics may be indicated, for example, by the received power of the received signal. Alternatively, the attenuation characteristics may be, for example, an attenuation rate. This signal may be, for example, a sinusoidal signal. The attenuation characteristics may be indicated, for example, by the transmission coefficient S21 of an S parameter. Alternatively, the transmission characteristics may be any information that can be used to determine, for example, a packet error rate. Specifically, since the packet acquisition rate can be known if the packet loss rate is known, the packet acquisition rate may be indicated by the packet loss rate.

[0028] 5A and 5B are diagrams showing measurement results for each frequency of the attenuation characteristics (transmission coefficient S21 of S parameters), which are transmission characteristics between two power line communication devices 10 in an automobile. The measurement results shown in FIGS. 5A and 5B were obtained using a network analyzer. S21 indicates the strength of a signal reaching a receiving device from a transmitting device at each frequency. FIGS. 5A and 5B each show the transmission characteristics for communication between two different points on the power line 2. As is clear from FIGS. 5A and 5B, if the communication path on the power line 2 is different, the transmission characteristics for each frequency will change significantly. Therefore, it is necessary to obtain the transmission characteristics for each device performing power line communication.

[0029] Next, the methods by which the identification unit 12 identifies a frequency band that has less attenuation than other frequency bands will be described for (1) the case where signals for multiple frequency bands are transmitted and received between devices, and (2) the case where packets for multiple frequency bands are transmitted and received between devices.

[0030] (1) When transmitting and receiving signals in multiple frequency bands between devices In this case, the power line communications device 10 on the transmitting side may transmit a probe signal of a predetermined transmission power using each of a plurality of frequency bands used in power line communications, and the power line communications device 10 on the receiving side may identify the received power of the probe signal for each of the plurality of frequency bands. Information indicating the received power or attenuation characteristics of the probe signal for each of the identified plurality of frequency bands may be transmitted to the power line communications device 10 on the transmitting side of the probe signal. The transmission may be performed, for example, using a specific frequency band (e.g., a frequency band with the best transmission characteristics or a predetermined frequency band), or may be performed using a plurality of frequency bands.

[0031] When information indicating the received power or attenuation characteristics of a probe signal for each of a plurality of frequency bands is transmitted from the power line communication device 10 on the receiving side of the probe signal to the power line communication device 10 on the transmitting side, the identifying unit 12 of the power line communication device 10 on the transmitting side may acquire the transmission characteristics for each frequency band by calculating them or by receiving them from the power line communication device 10 on the receiving side of the probe signal, and may identify a frequency band with less attenuation than other frequency bands using the acquired transmission characteristics. For example, the frequency band with the least attenuation may be identified. Note that when the power line communication device 10 on the receiving side of the probe signal transmits received power to the power line communication device 10 on the transmitting side, the identifying unit 12 of the power line communication device 10 on the transmitting side may calculate the attenuation characteristics for each of the plurality of frequency bands using the received power. Furthermore, the identifying unit 12 of the power line communication device 10 on the transmitting side of the probe signal may transmit information indicating a frequency band with less attenuation than other frequency bands to the power line communication device 10 on the receiving side via the communication unit 11. The identifying unit 12 of the power line communication device 10 on the receiving side may acquire a frequency band with less attenuation than other frequency bands contained in a signal transmitted from another power line communication device 10. In this case, the identifying unit 12 of the power line communication device 10 on the receiving side of the probe signal acquires the frequency band with less attenuation than other frequency bands, which corresponds to identifying the frequency band.

[0032] On the other hand, the identifying unit 12 of the power line communications device 10 on the probe signal receiving side may identify a frequency band with less attenuation than other frequency bands by using the attenuation characteristics of the probe signal for each of a plurality of frequency bands. In this case, the identifying unit 12 of the power line communications device 10 on the probe signal receiving side may transmit information indicating the frequency band with less attenuation than other frequency bands to the power line communications device 10 on the probe signal transmitting side via the communication unit 11. Then, the identifying unit 12 of the power line communications device 10 on the transmitting side may acquire the frequency band with less attenuation than other frequency bands, which is included in the signal transmitted from the other power line communications device 10. In this case, the identifying unit 12 of the power line communications device 10 on the probe signal transmitting side acquires the frequency band with less attenuation than other frequency bands, which corresponds to identifying the frequency band.

[0033] 6A and 6B are diagrams illustrating an example of how transmission characteristics change with frequency. Assuming that FIG. 6A shows the transmission characteristics of a power line 2 between a first device and a second device, when the frequency is 50 MHz, a signal is transmitted from the first device to the second device with a loss of approximately 10 dB. The same applies to communication from the second device to the first device. When the frequency is 100 MHz, the loss is approximately 40 dB. In other words, the loss amount is approximately 1000 times greater. Therefore, in the case of the transmission characteristics shown in FIG. 6A, it is preferable to perform power line communication in a frequency band around 50 MHz. On the other hand, in the case of the transmission characteristics shown in FIG. 6B, a frequency around 100 MHz results in less loss when a signal is transmitted from the first device to the second device than a frequency around 50 MHz. Therefore, in the case of the transmission characteristics shown in FIG. 6B, it is preferable to perform power line communication in a frequency band around 100 MHz.

[0034] (2) When transmitting and receiving packets for multiple frequency bands between devices In this case, the power line communications device 10 on the transmitting side may transmit predetermined probe packets using each of a plurality of frequency bands used in power line communications, and the power line communications device 10 on the receiving side may receive the probe packets and calculate the packet acquisition rate and packet error rate for each of the plurality of frequency bands. When the packet acquisition rate is calculated, it is preferable that a predetermined number of packets be transmitted. Information indicating the packet acquisition rate and packet error rate for each of the plurality of frequency bands may be transmitted to the power line communications device 10 on the probe packet transmitting side.

[0035] When information indicating a packet acquisition rate and a packet error rate for each of a plurality of frequency bands is transmitted from the power line communications device 10 on the receiving side of a probe packet to the power line communications device 10 on the transmitting side, the identifying unit 12 of the power line communications device 10 on the transmitting side may acquire the transmission characteristics for each frequency band by receiving them and identify a frequency band with less attenuation than other frequency bands using the acquired transmission characteristics. Furthermore, the identifying unit 12 of the power line communications device 10 on the transmitting side of a probe packet may transmit information indicating a frequency band with less attenuation than other frequency bands to the power line communications device 10 on the receiving side via the communication unit 11. The identifying unit 12 of the power line communications device 10 on the receiving side may then acquire a frequency band with less attenuation than other frequency bands, which is included in a signal transmitted from another power line communications device 10. In this case, the identifying unit 12 of the power line communications device 10 on the receiving side of a probe packet, acquiring a frequency band with less attenuation than other frequency bands, corresponds to identifying that frequency band. In addition, the number of received packets or the received packets themselves may be transmitted from the power line communication device 10 on the receiving side of the probe packets to the power line communication device 10 on the transmitting side, and the packet acquisition rate and packet error rate may be calculated in the power line communication device 10 on the transmitting side.

[0036] On the other hand, the identifying unit 12 of the power line communications device 10 on the receiving side of the probe packets may identify a frequency band with less attenuation than other frequency bands using the packet acquisition rate and packet error rate of the probe packets for each of the multiple frequency bands. In this case, the identifying unit 12 of the power line communications device 10 on the receiving side of the probe packets may transmit information indicating the frequency band with less attenuation than other frequency bands to the power line communications device 10 on the transmitting side via the communication unit 11. Then, the identifying unit 12 of the power line communications device 10 on the transmitting side may acquire a frequency band with less attenuation than other frequency bands that is included in a signal transmitted from another power line communications device 10. In this case, the identifying unit 12 of the power line communications device 10 on the transmitting side of the probe packets acquires a frequency band with less attenuation than other frequency bands, which corresponds to identifying the frequency band.

[0037] Note that, when the power line communications device 10 transmitting the probe packets transmits the probe packets at a predetermined transmission power, it is possible to acquire the same attenuation characteristics as in (1) above. Therefore, in this case (2), the identifying unit 12 may acquire the attenuation characteristics in addition to the packet acquisition rate and packet error rate. Note that, when a plurality of transmission characteristics (e.g., the packet acquisition rate and packet error rate, or the packet acquisition rate and attenuation characteristics) are acquired, a frequency band with less attenuation may be identified using, for example, a representative value of each value, or a frequency band with less attenuation may be identified using the result of weighted addition of each value. The representative value may be, for example, an average value, a maximum value, or a minimum value. Furthermore, when calculating the representative value or performing weighted addition, each value may be normalized, for example. This normalization may involve, for example, converting each value into a value ranging from 0 to 1, where the closer to 1 the value, the less attenuation there is.

[0038] Furthermore, the frequency band with less attenuation than other frequency bands is identified as a transmission path between devices performing power line communication. Typically, power line communication is performed between master device 1-1 and slave devices 1-2 to 1-N via power line 2, so a frequency band with less attenuation than other frequency bands is identified for each of the transmission paths between master device 1-1 and slave devices 1-2 to 1-N. For this reason, probe signals or probe packets may be transmitted from master device 1-1 to each of slave devices 1-2 to 1-N by broadcast, for example. Then, master device 1-1 may repeatedly transmit probe signals or the like while changing the frequency band, for example.

[0039] Each of identifying units 12-2 to 12-N of slave devices 1-2 to 1-N may identify only the frequency band used in power line communication with master device 1-1, for example. On the other hand, identifying unit 12-1 of master device 1-1 may identify the frequency band used in power line communication for each of slave devices 1-2 to 1-N, for example.

[0040] The communication control unit 13 controls the communication unit 11 to perform power line communication using the frequency band identified by the identification unit 12. For example, the communication control unit 13 may set the frequency band identified by the identification unit 12 to the communication unit 11 as the frequency band for performing power line communication. Then, the communication unit 11 may perform power line communication via the power line 2 using the set frequency band.

[0041] Control unit 14-1 of master device 1-1 may perform control to transmit information corresponding to an operation accepted by acceptance unit 20-1 to a corresponding device among slave devices 1-2 to 1-N via communication unit 11-1, for example.

[0042] Control unit 14-2 of slave device 1-2 may control operation of electrical device 20-2 in response to information received from master device 1-1 by communication unit 11-2. For example, if electrical device 20-2 is a motor for opening and closing a window, control unit 14-2 may operate electrical device 20-2, which is a motor, in the direction to open the window in response to an instruction to open the window received from master device 1-1. The same applies to the other slave devices 1-3 to 1-N.

[0043] Here, several examples of the communication unit 11 will be described. FIG. 7 is a diagram illustrating an example of the communication unit 11 connected to the power line 2. In FIG. 7, the communication unit 11 is connected to the power line 2 via a capacitor 15. With this configuration, the capacitor 15 can remove a DC component. The capacitor 15 may be included in, for example, the power line communication device 10. The communication unit 11 may also include a switch 111, a receiving unit 112, a transmitting unit 113, and a power line communication control unit 114. The switch 111 may be controlled by the power line communication control unit 114 to connect one of the receiving unit 112 and the transmitting unit 113 to the power line 2. For example, when receiving information via power line communication, the switch 111 may be controlled so that the receiving unit 112 is connected to the power line 2. On the other hand, when transmitting information via power line communication, the switch 111 may be controlled so that the transmitting unit 113 is connected to the power line 2. The reception frequency of the receiver 112 and the transmission frequency of the transmitter 113 may also be controlled by the power line communication control unit 114. For example, the power line communication control unit 114 may perform control so that transmission and reception are performed in the frequency band set by the communication control unit 113.

[0044] In FIG. 8 , the communication unit 11 is connected to the power line 2 via an impedance matching unit 16 so as to enable efficient transmission of signals to the power line 2. The impedance matching unit 16 may also have a function of removing DC components. The impedance matching unit 16 performs impedance matching between the communication unit 11 and the DC power line 2. This impedance matching may be performed automatically or manually, for example. From the viewpoint of dynamically changing the frequency band, it is preferable that the impedance matching unit 16 performs automatic impedance matching. The impedance matching unit 16 may be included in, for example, the power line communication device 10. By including the impedance matching unit 16, the power line communication device 10 can efficiently transmit signals to the power line 2 and efficiently receive signals from the power line 2.

[0045] 7 and 8, the transmission and reception frequencies are the same and switch 111 is used to switch between transmission and reception, but the transmission frequency and reception frequency may be different. If the transmission frequency band and reception frequency band can be made different, then by replacing switch 111 with a circulator, it becomes possible to transmit and receive simultaneously. It is preferable that the transmission and reception frequency bands are sufficiently apart.

[0046] Another example is where a module used in wireless communication is used in the communication unit 11. For example, the frequency of a 2.4 GHz wireless communication module may be shifted to 50 MHz, which is used in power line communication. In this case, down-conversion is performed during transmission, and up-conversion is performed during reception. FIG. 9 is a block diagram showing an example of such a communication unit 11. In FIG. 9, the communication unit 11 includes switches 121 and 122, an up-converter 123, a down-converter 124, and a wireless communication module 125.

[0047] The wireless communication module 125 controls the switches 121 and 122 via control lines indicated by dashed lines. For example, when receiving a signal, the wireless communication module 125 may control the switch 121 to connect the power line 2 to the upconverter 123, and the switch 122 to connect the upconverter 123 to the wireless communication module 125. For example, when transmitting a signal, the wireless communication module 125 may control the switch 121 to connect the power line 2 to the downconverter 124, and the switch 122 to connect the downconverter 124 to the wireless communication module 125. The wireless communication module 125 may also control the downconverter 124 or the upconverter 123 to downconvert a frequency band used in power line communication with a communication destination device, or to upconvert from that frequency band to the frequency band of the wireless communication module 125.

[0048] For example, when the communication control unit 13 sets the communication unit 11 to use a first frequency band in power line communication with a destination device, the wireless communication module 125 may set the upconverter 123 to upconvert a signal in the first frequency band to a 2.4 GHz signal and set the downconverter 124 to downconvert the 2.4 GHz signal to a signal in the first frequency band. When transmitting a signal to the destination device, the wireless communication module 125 may control the switches 121 and 122 to be connected to the downconverter 124 side. Thereafter, when the wireless communication module 125 outputs a 2.4 GHz transmission signal to the switch 122, the transmission signal is input to the downconverter 124, downconverted to the first frequency band, and output to the power line 2 via the switch 121. The transmission signal is then transmitted to the destination device via the power line 2.

[0049] Furthermore, when receiving a transmission signal transmitted in the first frequency band from a communication destination device, the wireless communication module 125 may control the switches 121 and 122 so that each is connected to the upconverter 123. When the transmission signal is input to the upconverter 123 via the power line 2 and the switch 121, the upconverter 123 may upconvert the transmission signal to 2.4 GHz and output it to the switch 122. The upconverted transmission signal is received by the wireless communication module 125 via the switch 122.

[0050] In this way, power line communication can be realized by using the upconverter 123, the downconverter 124, and the wireless communication module 125. In this case, for example, the wireless communication module 125 for each power line communication device 10 may transmit and receive signals on different 2.4 GHz channels. This prevents the power line communication device 10 on the transmitting side from being connected to the power line communication device 10 on the receiving side from being connected both wirelessly and wired. If the two devices were connected both wirelessly and wired, a phenomenon similar to multipath would occur, resulting in a decrease in communication quality. However, by changing the frequency (channel) used by the wireless communication module 125 for each power line communication device 10, such a problem can be prevented. Note that it is natural that the frequency band of signals transmitted via the power line 2 is the same for the power line communication device 10 on the transmitting side and the power line communication device 10 on the receiving side. Although several examples of the communication unit 11 have been described, it goes without saying that the communication unit 11 is not limited to these examples and may have other configurations.

[0051] Next, the operation of the power line communication device 10 will be described with reference to the flowchart of FIG. (Step S101) The communication unit 11 determines whether to communicate. If communication is to be performed, the process proceeds to step S102; if not, the process proceeds to step S103. The determination of whether to communicate may be, for example, a determination of whether information transmitted from another device has been received, or a determination of whether to transmit information to another device. In the latter case, the communication unit 11 may determine to transmit information to another device, for example, when there is information to transmit to the other device (for example, when there is information in a transmission queue).

[0052] (Step S102) The communication unit 11 performs processing related to communication. For example, if it is determined in step S101 that information has been received, the communication unit 11 may pass the received information to the control unit 14 or to another component. Also, for example, if it is determined in step S101 that information is to be transmitted, the communication unit 11 may transmit the information to be transmitted to a destination device via power line communication. Then, the process returns to step S101.

[0053] (Step S103) The identifying unit 12 determines whether to identify a frequency band with less attenuation. If a frequency band with less attenuation is to be identified, the process proceeds to step S104; if not, the process returns to step S101. Note that, for example, the identifying unit 12-1 of the master device 1-1 may determine to identify a frequency band with less attenuation periodically (for example, every 10 minutes, every 30 minutes, or every hour). Also, for example, the identifying units 12-2 to 12-N of the slave devices 1-2 to 1-N may determine to identify a frequency band with less attenuation when the communication unit 11 receives a probe signal or probe packet transmitted from the master device 1-1.

[0054] (Step S104) The identifying unit 12 identifies a frequency band with less attenuation. For example, the identifying unit 12-1 of the master device 1-1 may cause the communication unit 11-1 to transmit a probe signal or a probe packet, and identify a frequency band with less attenuation using information received from each of the slave devices 1-2 to 1-N in response to the transmission. The identified frequency band may then be transmitted to each of the slave devices 1-2 to 1-N. For example, the identifying units 12-2 to 12-N of the slave devices 1-2 to 1-N may acquire transmission characteristics in response to receiving a probe signal or a probe packet, transmit the acquired transmission characteristics to the master device 1-1 via the communication units 11-2 to 11-N, and acquire the frequency band with less attenuation transmitted from the master device 1-1 and received by the communication units 11-2 to 11-N in response to the transmission.

[0055] (Step S105) The communication control unit 13 sets the frequency band with less attenuation identified in step S104 as the frequency band to be used in power line communication in the communication unit 11. Then, the process returns to step S101.

[0056] Although the flowchart of Fig. 2 does not include processing related to the control unit 14, it goes without saying that processing by the control unit 14 may be performed as appropriate. Also, the order of processing in the flowchart of Fig. 2 is an example, and the order of each step may be changed as long as the same results are obtained. Also, in the flowchart of Fig. 2, processing ends when the power is turned off or an interrupt to end processing occurs.

[0057] Next, the operation of power line communication system 100 according to this embodiment will be described using a specific example. In this specific example, it is assumed that N=5. That is, it is assumed that four slave devices 1-2 to 1-5 are connected to power line 2. In this specific example, it is assumed that the frequency band is the communication channel and the transmission characteristic is the packet acquisition rate.

[0058] First, assume that the power line communication system 100 is started. For example, the power line communication system 100 may be started when the mobile object 4, which is an automobile, starts. When the power line communication system 100 is started, the identifying unit 12-1 of the master device 1-1 determines to identify a communication channel with less attenuation (step S103) and transmits a predetermined number of probe packets by broadcast from the first communication channel to each of the slave devices 1-2 to 1-5 via the communication unit 11-1. The identifying unit 12-1 also transmits the predetermined number of probe packets in the same manner for multiple communication channels, such as the second communication channel and the third communication channel.

[0059] The probe packets transmitted in this manner are received by each of the slave devices 1-2 to 1-5 (step S101) and passed to the identifying units 12-2 to 12-5 (step S102). Upon receiving the probe packets, the identifying units 12-2 to 12-5 determine that a communication channel with less attenuation has been identified (step S103), count the number of received probe packets for each communication channel, calculate a packet acquisition rate, and transmit the calculated packet acquisition rate for each communication channel to the master device 1-1 via the communication units 11-2 to 11-5. Preferably, the calculated packet acquisition rate for each communication channel is transmitted to the master device 1-1 together with the identifier of each of the slave devices 1-2 to 1-5. This is to enable the master device 1-1 to identify the slave device that transmitted the probe packets.

[0060] The packet acquisition rate for each communication channel and the identifier of each device transmitted from each of the slave devices 1-2 to 1-5 are received by the communication unit 11-1 of the master device 1-1 and passed to the identification unit 12-1. For each of the slave devices 1-2 to 1-5, the identification unit 12-1 identifies the communication channel with the highest packet acquisition rate using the packet acquisition rate of each communication channel and designates that communication channel as the communication channel with less attenuation than the other communication channels. The identification unit 12-1 then transmits the identified communication channel corresponding to each of the slave devices 1-2 to 1-5 via the communication unit 11-1 (step S104). The identification unit 12-1 also passes information associating the identified communication channel with the identifier of the slave device to the communication control unit 13-1. The communication control unit 13-1 then sets the information in the communication unit 11-1 (step S105).

[0061] The communication channel transmitted from master device 1-1 is received by communication units 11-2 to 11-5 of slave devices 1-2 to 1-5 and passed to identification units 12-2 to 12-5, respectively (step S104). The received communication channel is then passed from identification units 12-2 to 12-5 to communication control units 13-2 to 13-5, respectively, and set in communication units 11-2 to 11-5, respectively, as the communication channel to be used in power line communication (step S105).

[0062] Thereafter, for example, when power line communication is performed between master device 1-1 and slave device 1-2, communication unit 11-1 of master device 1-1 uses the communication channel associated with the identifier of slave device 1-2 and the communication channel set in communication unit 11-2 of slave device 1-2. For example, when control information for opening and closing a window is transmitted from master device 1-1 to slave device 1-2, the control information may be transmitted from communication unit 11-1 using the communication channel associated with the identifier of slave device 1-2.

[0063] As described above, in power line communications device 10 according to the present embodiment, identifying unit 12 identifies a frequency band with less attenuation than other frequency bands, and performs power line communications using the identified frequency band, thereby enabling communication with less signal attenuation, i.e., high-quality communication, in power line communications via power line 2 in a mobile object. Therefore, for example, master device 1-1 can transmit information accurately to slave devices 1-2 to 1-N, enabling more accurate control. Furthermore, by repeatedly identifying frequencies with less attenuation, even if the frequency of interfering radio waves changes as the mobile object moves, for example, it becomes possible to dynamically select a suitable frequency band in response to the change and perform power line communications.

[0064] In the present embodiment, the case where information is transmitted via power line communication from master device 1-1 to slave devices 1-2 to 1-N mainly for the purpose of controlling electrical appliance 20-2 and the like has been described. However, this is not necessarily the case. For example, power line communication device 10 does not have to be included in master device 1-1 or slave devices 1-2 to 1-N. Furthermore, even when power line communication is performed between any two or more power line communication devices 10 installed in a mobile object, a frequency band with less attenuation than other frequency bands may be identified, as described above, and power line communication may be performed using the identified frequency band. Furthermore, power line communication may be performed for purposes other than controlling electrical appliances. For example, power line communication may be performed to transmit video captured by a camera to a monitor device or a recording device. More specifically, power line communication via power line 2 may be performed to transmit video captured by a backup camera of an automobile to a monitor or a recording device inside the automobile.

[0065] Furthermore, in the above embodiments, each process or function may be realized by centralized processing by a single device or a single system, or may be realized by distributed processing by multiple devices or multiple systems.

[0066] Furthermore, the present invention is not limited to the above-described embodiment, and various modifications are possible, and it goes without saying that these modifications are also included within the scope of the present invention. [Explanation of symbols]

[0067] 2. Power lines 10, 10-1~10-N power line communication equipment 11, 11-1~11-N Communications Department 12, 12-1~12-N Specific part 13, 13-1 to 13-N Communication control unit 16 Impedance matching section

Claims

1. A master power line communication device that performs power line communication with a plurality of slave power line communication devices using a power line of a DC power supply in a mobile object, a communication unit that performs power line communication with a plurality of slave power line communication devices using a DC power line; an identifying unit that identifies, for each of a plurality of slave power line communication devices, a frequency band that has less attenuation than other frequency bands from among a plurality of frequency bands used in the power line communication; a master power line communication device comprising: each of the plurality of slave power line communication devices; and a communication control unit that controls the communication unit so as to perform power line communication using a frequency band identified for each of the plurality of slave power line communication devices.

2. The master power line communication device according to claim 1 , wherein the specifying unit repeatedly specifies a frequency band that has less attenuation than other frequency bands.

3. 3. The master power line communication device according to claim 1, wherein the specifying unit acquires transmission characteristics for each frequency band and uses the transmission characteristics to specify a frequency band that has less attenuation than other frequency bands.

4. The master power line communication device according to claim 3 , wherein the transmission characteristics are a packet error rate, a packet acquisition rate, or an attenuation characteristic.

5. 3. The master power line communication device according to claim 1, wherein the specifying unit acquires information indicating a frequency band that is less attenuated than other frequency bands, the information being included in a signal transmitted from the other power line communication device.

6. 1. A power line communication method for performing power line communication with a plurality of slave power line communication devices using a power line of a DC power supply in a mobile object, comprising: identifying a frequency band having less attenuation than other frequency bands from among a plurality of frequency bands used in the power line communication for each of a plurality of slave power line communication devices; and performing power line communication using a DC power line with each of the plurality of slave power line communication devices in a frequency band identified for each of the plurality of slave power line communication devices.

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