Vehicular power line communication system

A vehicular power line communication system includes a master and a slave. The master uses a pair of twisted wires, whose far ends are connected to each other to be loop-shaped, as a power line and a communication line. The master thereby outputs high-frequency signals via the pair of twisted wires, transmitting an electric power and data modulation signals. The slave includes an aperture antenna being loop-shaped to receive data modulation signals using an electromagnetic induction connection in an electromagnetic field generated in the pair of twisted wires in response to an energization current of the pair of twisted wires. The slave further includes an error rate monitor circuit which monitors an error rate of data which are obtained from demodulation of the data modulation signals received via the aperture antenna.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2012-27142 filed on Feb. 10, 2012, the contents of which are incorporated herein by reference.

FIELD

The present disclosure relates to a vehicular power line communication system where communicators communicate using power lines.

BACKGROUND

There are known ECUs (Electronic Control Units) in a vehicle to communicate with each other to thereby perform various controls in the vehicle smoothly. Therefore, the introduction of the power line communication (PLC) system is considered. This power line communication system is a technology which superimposes signals on high frequency carriers to thereby transmit and communicate.

For instance, Patent Literature 1 describes a technology where a moving object is equipped with a balanced feeder line composed of two parallel wire lines. The balanced feeder line is in proximity of a coupler shaped of a loop. Thereby, the moving object and the balanced feeder line form an electromagnetic induction connection (i.e., coupling) therebetween.

The inventors find the following. The above known technology enables electromagnetic induction connection and transmission of electric power and signals; however, there is much leakage flux in other than connection portions which transmit and receive the electric power and the signals. In addition, when a system environment changes, a communication quality may deteriorate to make it difficult to maintain high speed communication.

SUMMARY

It is an object of the present disclosure to provide a vehicular power line communication system which strengthens an electromagnetic induction connection using a power line between a transmission side and a reception side to provide a high-quality and high-speed power line communication in response to a system environment.

According to an aspect of the present disclosure, a vehicular power line communication system includes a master and a slave. The master includes a pair of twisted wires. The ends of the pair of twisted wires are connected to form a loop shape. The pair of twisted wires serves as a power line and a data communication line. The master further includes a modulation portion which modulates data to prepare a data modulation signal. The master outputs a high-frequency signal via the pair of twisted wires to transmit an electric power as well as the data modulation signal. The slave includes an aperture antenna having a loop shape to receive a data modulation signal via the pair of twisted wires using an electromagnetic induction connection with an electromagnetic field generated in the pair of twisted wires according to an energization current of the pair of twisted wires. The aperture antenna has a slave-side opening area that faces a master-side opening area provided in between twisted portions in the pair of twisted wires. The slave further includes a demodulation portion which demodulates the data modulation signal received via the aperture antenna to obtain a demodulated data. The slave further includes an error rate monitor portion which monitors an error rate of the demodulated data obtained by the demodulation portion.

The aperture antenna of the slave has the opening area that faces the opening area provided in between twisted portions included in the pair of twisted wires. Therefore, the power line communication may be achieved by strengthening an electromagnetic induction connection. Further, the use of the pair of twisted wires decreases leakage magnetic flux. In addition, the slave includes the demodulation portion which demodulates data modulation signals via the aperture antenna, and the error rate monitor portion which monitors the error rate of the demodulated data that is obtained by the demodulation by the demodulation portion. The measurement result of the error rate may be reflected on the communication process. This achieves a high-speed modulation and demodulation type within a range of error rates accepted by the system and provides a high-quality and high-speed power line communication in response to an environment of the system.

DETAILED DESCRIPTION

First Embodiment

The following explains a first embodiment of the present disclosure with reference toFIGS. 1 to 13. A vehicular power line communication system1includes a master (master-side system)2and slaves (slave-side systems)3A to3Z. The master2is connected with a battery (not shown). This master2supplies electric power to several slaves3A to3Z via the power line based on electric power of the battery. The several slaves3A to3Z operate based on the supplied electric power. The slaves3A to3Z are connected with loads5A to5Z that are composed of sensors and actuators, respectively. Hereinafter, each of the several slaves3A to3Z may be referred to as a slave3A to3Z.

The master2contains a communicator main body (master main body)2fand a pair of twisted wires4, which is connected with the communicator main body2f. The communicator main body2fincludes a control circuit (a modulation frequency control portion, a modulation and demodulation type control portion)2awhich controls communications and other functions; a high-frequency power generation circuit2b; a modulation and demodulator circuit (also referred to as a modem circuit or a modulation portion)2c; a superimposition and separation circuit2d; and a matching circuit (matching portion)2e. The control circuit2amainly includes a microcomputer. The high-frequency power generation circuit2bgenerates high-frequency signals (carrier wave signals) having a predetermined frequency, and outputs the generated high-frequency signals to the superimposition and separation circuit2das power signals.

The modulation and demodulation circuit2cchanges communication frequencies or modulation and demodulation types according to controls of the control circuit2a. The modulation and demodulation circuit2cmodulates communication data of the master2to prepare modulated data and outputs the modulated data to the superimposition and separation circuit2das data modulation signals. The superimposition and separation circuit2dmixes the carrier wave signals and data modulation signals and outputs the mixed data to the matching circuit2e. The matching circuit2etransmits, to the pair of twisted wires4, power and data modulation signals, i.e., high-frequency signals that are the carrier wave signals on which the data modulation signals are superimposed.

The control circuit2aconnects a control line to the matching circuit2e, thereby adjusting an impedance match status of the matching circuit2e. In addition, the control circuit2aconnects a control line to the modulation and demodulation circuit2c, thereby controlling a data modulation and demodulation type and data communication frequency of the modulation and demodulation circuit2cand functioning as a communication frequency control portion and a data modulation and demodulation control portion.

With reference to (a) to (d) inFIG. 2, the following will explain examples of configurations of the matching circuit2e. The matching circuit2eincludes a transformer2gand a variable capacity capacitor2h, which is connected to a primary side and/or a secondary side of the transformer2gin series or in parallel. The matching circuit2emay have any circuit configuration as long as providing an impedance match.

FIG. 3illustrates a perspective view of a pair of twisted wires4. The twisted wires4are extended from an output terminal of the main body2finstalled in the vehicle to a farthest end by about one meter. As illustrated inFIGS. 1,3, the pair of twisted wires4has a loop shape in which the farthest ends of the twisted wires (i.e., core wires) are connected or combined. In the present embodiment, the communication line composed of the twist wires having a special shape of the farthest ends combined is referred to as a pair of twisted wires4or the twisted wires4.

With reference toFIG. 1, the slave3A to3Z (namely, each slave) contains a control circuit3a, a modulation and demodulation circuit (demodulation portion)3c, a power-supply matching circuit3d, a communication matching circuit (matching portion)3e, a rectification circuit3f, and an error rate monitor circuit3g(error rate monitor portion). The power-supply matching circuit3dis connected with an aperture antenna3hfor electric power reception; the communication matching circuit3eis connected with an aperture antenna3ifor data reception.

The aperture antennas3hand3ihave a loop shape such as a circle, and receive an electromagnetic field generated in the above-mentioned twisted wires4via an electromagnetic induction connection. Therefore, the slaves3A, . . .3Z receive via the aperture antennas3hand3i, the electric power and the data modulation signals which the main body2fof the master2transmits, respectively.

With reference to (e) to (f) inFIG. 2, the following will explain examples of an equivalent circuit of the power-supply matching circuit3din the reception side. The power-supply matching circuit3dis a matching circuit which connects a fixed capacity capacitor3jto the aperture antenna3hin parallel or in series, and matches a transmission frequency band (for example, 10.7 MHz band) of power signals having high frequencies.

With reference to (g) to (h) inFIG. 2, the following will explain examples of an equivalent circuit of the communication matching circuit3ein the reception side. The communication matching circuit3eis a matching circuit which connects a variable capacity capacitor3kto the aperture antenna3iin parallel or in series. The communication matching circuit3echanges a capacity value of the variable capacity capacitor3kdepending on control of the control circuit3a, and provides an impedance matching to a predetermined frequency band (several tens of MHz band) higher than the above-mentioned frequency power supply band.

FIG. 4illustrates transfer characteristics of the matching circuit2ein the master2.FIG. 5AandFIG. 5Billustrate transfer characteristics of the communication matching circuit3eand the power-supply matching circuit3dof the slaves3A, . . .3Z, respectively. The frequency band for power supply (for example, 10.7 MHz band) and the frequency band for data communications (tens of MHz band) are separate from each other. This may provide the matching circuit2e, the power-supply matching circuit3d, and the communication matching circuit3ewith suitable frequency bands and suitable transfer characteristics. In the present embodiment, the bit rate of the data communication is comparatively high; therefore, the frequency band of the data communication is provided to be higher than the frequency band for power supply (10.7 MHz band). However, if the bit rate is low, the frequency band for data communications may be provided to be lower than the frequency band for power supply.

Returning toFIG. 1, upon receiving high-frequency signals for power supply, the power-supply matching circuit3doutputs them to the rectification circuit3f. The rectification circuit3frectifies the electric power AC signals to form direct current power. The direct current power is supplied to the modulation and demodulation circuit3c, the error rate monitor circuit3g, the control circuit3a, and the load5A.

The modulation and demodulation circuit3coperates on direct current power supplied from the rectification circuit3f. The modulation and demodulation circuit3creceives a data modulation signal via the aperture antenna3i, which is matched with a predetermined frequency band for data communication by the communication matching circuit3e. The modulation and demodulation circuit3cdemodulates the data modulation signal to obtain a demodulated data using the communication frequency and the modulation and demodulation type which are controlled by the control circuit3a, and outputs the demodulated data to the error rate monitor circuit3g. The control circuit3acontrols the communication frequency and the modulation and demodulation type of the modulation and demodulation circuit3c, and functions as a communication frequency control portion and a data modulation and demodulation control portion.

The error rate monitor circuit3goperates on direct current power supplied from the rectification circuit3f. The error rate monitor circuit3gcalculates an error rate of the demodulated data which is demodulated by the modulation and demodulation circuit3c, and transmits it to the control circuit3a. The control circuit3aoperates on direct current power supplied from the rectification circuit3f. The control circuit3areceives the demodulated data which is demodulated by the modulation and demodulation circuit3c, and operates the load5A. Such an operation takes place in each of slaves3A, . . .3Z, equivalently. Thereby, the data may be transmitted from the master2to the slaves3A, . . .3Z.

In contrast, the slaves3A, . . .3Z transmit data as follows. The control circuit3amodulates data to form a modulation signal using the modulation and demodulation circuit3cand outputs the modulation signal to the aperture antenna3iusing the communication matching circuit3e. The aperture antenna3ioutputs the modulation signal as a radio wave signal.

The twisted wires4are extended from the main body2fof the master2to proximity of each of the slaves3A, . . .3Z. The twisted wires4are a twisted-pair cable of UTP (unsealed twisted pair), for example. At the time of signal transmission by the master2, the energization current by the high-frequency signal generates magnetic fluxes in between adjoining twisted portions4A,4B, . . . and the adjoining magnetic fluxes are reverse to each other to cancel each other, helping prevent the external output of noises. In contrast, at the time of signal reception of the master2, a pair of twisted wires4have few flux linkage regions in response to radio waves coming from outside, thereby being less vulnerable to the radio waves. Therefore, this configuration is suitable for suppressing the noise generation and eliminating noises coming from the outside.

Among several opening areas between the several twisted portions4A, . . . in the twisted wires4, an opening area in between the twisted portions4A and4B faces the aperture antenna3hof the slave3A. In addition, an opening area in between the twisted portions4C and4D faces the aperture antenna3iof the slave3A.

In order to illustrate arrangement positions of the twisted portions4A,4L inFIG. 1, the opening areas of the twisted wires4(in between the twisted portions4A to4B,4E to4F, . . . ,4I to4J) and the opening areas of the aperture antennas3hare opposite with respect to x direction alone.

Further, the opening areas of the twisted wires4(in between the twisted portions4C to4D,4G to4H, . . . ,4K to4L) and the opening areas of the aperture antennas3iare opposite with respect to x direction alone. However, they are opposite actually with respect to y direction, too, as illustrated inFIG. 3. Thus, the opening areas of the twisted wires4and the openings of the aperture antennas3hor aperture antennas3ioverlap.

Therefore, the electromagnetic field generated in each of the opening areas in between the twisted portions (4A,4B, . . . ,4G,4H, . . . ,4K,4L) of the twisted wires4forms an electromagnetic induction connection with each of the aperture antennas3h.3iof the slaves3A, . . . ,3Z. Each aperture antenna3h,3iof the slaves3A, . . . ,3Z may receive electric power and data modulation signals in a contactless manner via the electromagnetic field produced in the opening areas in between twisted portions4A to4B, . . . ,4K to4L of the twisted wires4.

Thereby, each slave3A, . . . ,3Z can receive the data modulation signals as well as the power signals for power supply favorably. Further, each slave3A, . . . ,3Z can also transmit reply signals favorably. In addition, when each slave3A, . . . ,3Z transmits reply signals from the aperture antenna3i, the master2can receive the reply signals in a contactless manner via the opening areas in between the twisted portions (4A,4B, . . . ,4G,4H, . . . ,4K,4L) of the twisted wires4.

In addition, the twisted wires4may be provided such that only regions or opening areas in between the twisted portions4A to4B,4C to4D, . . . ,4K to4L that face the aperture antennas3hand3iof each slave3A, . . . ,3Z are larger than other regions or opening areas. This configuration is suitable for suppressing noise generation and eliminating noises coming from the outside while strengthening an electromagnetic induction connection between the twisted wires4and the aperture antennas3hand3i.

FIGS. 6A,6B illustrate examples of an error rate detected by the error rate monitor circuit3g. In the drawings, Eb is a maximum allowable error rate of the system1;

Ea is an upper limit of the error rate that provides a high quality communication. When the reception error rate exceeds Eb as illustrated inFIG. 6A, the matching characteristic is adjusted in the matching circuit2eand the communication matching circuit3e, or the communication frequency of the communication carrier are changed in the modulation and demodulation circuits2cand3c(F0→FN), thereby reducing the error rate to achieve a high quality communication as illustrated inFIG. 6B. In addition, the modulation and demodulation type of the modulation and demodulation circuits2cand3cmay be changed.

The master2operates in a usual mode or an adjustment mode.

The master2communicates in the power line communication with the slaves3A, . . . ,3Z in the normal mode. At a start-up or activation, the master2moves to the adjustment mode that includes a communication frequency adjustment mode and a modulation and demodulation type adjustment mode, thereby adjusting a communication frequency (communication carrier frequency of the modulation and demodulation circuits2cand3c), a matching characteristic, and a modulation and demodulation type which are used for power line communication. In such a case, the slaves3A to3Z perform communication feedback to the master2, and communicate data using the data communication frequency band. The communication frequency, the matching characteristic, and the modulation and demodulation mode are adjusted between the master2and the slaves3A to3Z.

The master2performs adjustments with all the slaves3A to3Z in the communication frequency adjustment mode and modulation and demodulation type adjustment mode. After completing the adjustments with all the slaves3A to3Z, a usual power line communication process is performed. An adjustment process in the communication frequency adjustment mode and the modulation and demodulation type adjustment mode will be explained as a feature of the present embodiment. It is further noted that a flowchart in the present application includes sections (also referred to as steps), which are represented, for instance, as S1, T1, or the like. Further, each section can be divided into several sections while several sections can be combined into a single section. Furthermore, each of thus configured sections can be referred to as a module, device, or means and achieved not only (i) as a software section in combination with a hardware unit (e.g., computer), but also (ii) as a hardware section, including or not including a function of a related apparatus. Further, the hardware section may be inside of a microcomputer.

The following will explain an operation in the adjustment mode between the master2and the slaves3A to3Z with reference toFIGS. 7,8. When the master2starts, the modulation and demodulation circuit2cinitially sets a communication frequency F (=F0: communication carrier frequency) in response to a frequency instruction of the control circuit2a(S1). The data is modulated with a prescribed modulation and demodulation type (for example, BPSK (Binary Phase Shift Keying)) on the carrier of the set communication frequency F. The superimposition and separation circuit2dsuperimposes the data modulation signal of the modulation and demodulation circuit2con the power signal outputted by the high-frequency power generation circuit2b, thereby outputting to the twisted wires4via the matching circuit2e.

At this time, the master2moves to the adjustment mode of the communication frequency F when outputting the signal (the power signal, the data modulation signal) to the twisted wires4first after starting (S2), then waiting for replay signals from the slaves3A to3Z. At this time, when the number of the slaves3A to3Z connected to the master2is N, the master2waits until receiving ACKBPSK (k) (k=1 to Z) from all the N slaves3A to3Z (S3).

In contrast, as illustrated inFIG. 8, after starting, each slave3A to3Z receives an output signal of the master2; the output signal includes a power signal and a data modulation signal (T1). Then, each slave3A to3Z moves to the adjustment mode of the communication frequency F (T2). In the adjustment mode, each slave3A to3Z demodulates the BPSK modulated data with the modulation and demodulation circuit3c, and determines whether the error rate E(BPSK) of the demodulated data is less than a predetermined threshold level Eth1(T3) using the error rate monitor circuit3g. It is noted that the threshold level Eth1is equivalent to a first predetermined level and indicates a threshold level of the error rate which the system1can permit. Further, the threshold level Eth1is equivalent to Eb inFIG. 6Aor a threshold level with a margin against Eb. More preferably, the threshold level Eth1may be equivalent to Ea inFIG. 6Benabling a high quality communication or a threshold level with a margin against Ea.

When the error rate E(BPSK) of the demodulated data is less than the predetermined threshold level Eth1, each slave3A to3Z transmits ACKBPSK(k) (k=1 to Z) to the master2as a reply signal (T4), and advances to the modulation and demodulation type adjustment mode (T5).

When receiving ACKBPSK (k) from the slave3A (S3: YES), the master2completes the adjustment of the communication frequency (S4), ending the communication frequency adjustment mode and advancing to the modulation and demodulation type adjustment mode (S5).

In contrast, when the error rate E(BPSK) of the demodulated data exceeds the predetermined threshold level Eth1(T3: NO), each slave3A to3Z performs a matching process (T6). The impedance match may be insufficient at the beginning of the adjustment mode; thus, the error rate E(BPSK) of the data received by the slave3A to3Z may be too high.

When the error rate E(BPSK) exceeds the predetermined level Eth1, the matching process is performed (T6). When the capacity value of the variable capacity capacitor3kis adjusted step by step, the error rate E(BPSK) of the data received by the slave3A may be made low.

When the error rate E(BPSK) of the received data is made less than the predetermined threshold level Eth1according to the matching adjustment with the communication matching circuit3e(T3: YES), the control circuit3atransmits ACKBPSK(k) (T4), and advances to the modulation and demodulation type adjustment mode (T5).

Although waiting until receiving ACKBPSK (k) from all the N slaves3A to3Z, the master2may eventually not receive ACKBPSK(k) from all the slaves3A to3Z. In such a case, the master2changes the communication carrier frequency F one by one (F=F0→F1→F2→ . . . →Fn: S6).

This permits the slaves3A to3Z to decrease the error rate E(BPSK) of the received data. When the error rate E(BPSK) becomes less than the threshold level Eth1at T3inFIG. 8, the control circuit3atransmits ACKBPSK (k) at T4. The slave3A to3Z advances to the modulation and demodulation type adjustment mode at T5.

The following will explain operations of the master2(control circuit2a) and the slave3A to3Z (control circuit3a) in the modulation and demodulation type adjustment mode after the end of the communication frequency adjustment mode with reference toFIG. 9andFIG. 10.

As illustrated in the master side operation inFIG. 9, when advancing to the modulation and demodulation type adjustment mode, the master2increases the communication data rate first. To that end, the master2changes the modulation and demodulation type of the modulation and demodulation circuit2cfrom BPSK to QPSK (Quadrature Phase Shift Keying) at U1to increase the number of assignment data per symbol by one level. That is, the number of assignment data per one symbol of BPSK is two data per symbol; the number of assignment data per symbol of QPSK is four data per symbol. The master2transmits the modulated data to the slaves3A to3Z. The information on the modulation and demodulation type is assigned to the communication header and transmitted to the slaves3A to3Z.

In contrast, the slaves3A to3Z calculates the error rate E(QPSK) of the QPSK-demodulated data as illustrated inFIG. 10, and determines whether the error rate E(QPSK) is less than a threshold level Eth2(at V1).

The threshold level Eth2has a value that is equal to or greater than the Eth1and equivalent to a second predetermined level. The threshold level Eth2may be the maximum error rate Eb allowable in the system1or a predetermined level with a margin against Eb. More preferably, the threshold level Eth2may be the error rate Ea enabling a high quality communication or a predetermined level with a margin against Ea. That is. the slaves3A to3Z determines whether to receive the QPSK-modulated data. Each slave3A to3Z transmits ACKQPSK(k) (k=1 to Z) to the master2at V2when the conditions at V1is satisfied.

In contrast, when the control circuit3adetermines that the error rate E(QPSK) is less than the threshold level Eth2at V1, counts the number of matching times m1, dividing the process depending on the counting result. For example, it is determined whether the number of matching times m1 is greater than a predetermined number of times M1 (at V3).

The number of matching times m1 signifies the number of times the communication matching circuit3eperforms the matching process with the aperture antenna3idepending on control by the control circuit3a. The control circuit3astores this number of matching times m1. When moving to the QPSK modulation and demodulation type, the error rate may be high. In such a case, the matching process is performed at V4, where the capacity value of the variable capacity capacitor3kis adjusted step by step. The error rate of the data received by the slaves3A to3Z may be gradually made low.

Thus, when the error rate E(QPSK) becomes less than the predetermined threshold level Eth2in response to the matching process at V4by the communication matching circuit3e(V1: YES), the slaves3A to3Z transmit ACKQPSK(k) to the master2at V2.

In contrast, when the error rate E(QPSK) remains not less than the predetermined threshold level Eth2regardless of equal to or greater than a predetermined number of matching times M1 (V3: YES), QPSK is changed to BPSK in order to decrease the number of communications data per symbol by one step at V5. Then, the modulation and demodulation type adjustment mode is ended.

As illustrated inFIG. 9. when the master2receives ACKQPSK(k) (k=1 to Z) from all the slaves3A to3Z (U2: YES), the modulation and demodulation type of the modulation and demodulation circuit2cis changed to increase the data rate. That is, QPSK is changed to 16QAM (16 Quadrature Amplitude Modulation). The number of assignment data per symbol of 16QAM type is sixteen data per symbol; the number of assignment data per symbol of QPSK is four data per symbol. Then, the 16QAM-modulated data are transmitted to the slaves3A to3Z; then, the master2waits.

When any one of the slaves3A to3Z does not transmit ACKQPSK(k), the master2naturally does not receive ACKQPSK(k) from all the slaves3A to3Z. At this time, the master2selects BPSK as a communication phase (at U4), and ends the modulation and demodulation type adjustment mode. In this case, the master2notifies all the slaves3A to3Z that BPSK is selected as a communication phase.

The master2transmits the 16QAM-modulated data to the slaves3A to3Z. The slaves3A to3Z calculates the error rate(16QAM) E of the 16QAM-demodulated data using the error rate monitor circuit3g, and determines whether the error rate E(16QAM) is less than a threshold level Eth2(at V6).

That is, the slaves3A to3Z determine whether to receive the 16QAM-modulated data. The control circuit3aof each slave3A to3Z transmits ACKQPSK(k) (k=1 to Z) to the master2at V7when the conditions at V6is satisfied.

In contrast, when it is determined that the error rate E(16QAM) is less than the threshold level Eth2at V6, the number of matching times m2 is counted, and the process branches depending on this counting result. For example, it is determined whether the number of matching times m2 is equal to or greater than the predetermined number of times M2 (at V8).

The number of matching times m2 signifies the number of times the communication matching circuit3eperforms the matching process with the aperture antenna3idepending on control by the control circuit3a. The control circuit3astores this number of matching times m2. The error rate may be high when the modulation and demodulation type is changed into the 16QAM modulation and demodulation type. In such a case, the matching process is performed by the communication matching circuit3e(at V9). When the capacity value of the variable capacity capacitor3kis adjusted step by step, the error rate E of the data received by the slave3A to3Z may be made low.

Thus, when the error rate E(16QAM) becomes less than the predetermined threshold level Eth2in response to the matching process at V9by the communication matching circuit3e(V6: YES), ACK16QAM(k) is transmitted to the master2(at V7).

In contrast, when the error rate E(16QAM) remains not less than the predetermined threshold level Eth2regardless of equal to or greater than a predetermined number of matching times M2 (V8: YES), 16QAM is changed to QPSK in order to decrease the number of communications data per symbol by one step at V10. Then, the modulation and demodulation type adjustment mode is ended.

As illustrated inFIG. 9, when receiving ACK16QAM(k) (k=1 to Z) from all the slaves3A to3Z (U5: YES), the master2changes the data rate from 16QAM to 64QAM (i.e., 16 data per symbol→64 data per symbol) at U6. Then, the 64QAM-modulated data are transmitted to the slaves3A to3Z.

However, when any one of the slaves3A to3Z does not transmit ACK16QAM(k), the master2naturally does not receive ACK16QAM(k) from all the slaves3A to3Z. In this case, 16QAM is changed to QPSK in order to decrease the number of communication data per symbol by one step at U7. Then, the modulation and demodulation type adjustment mode is ended. In this case, the master2notifies all the slaves3A to3Z that QPSK is selected as a communication phase.

The master2transmits the 64QAM-modulated data to the slaves3A to3Z. As illustrated inFIG. 10, in the slaves3A to3Z, the error rate E(64QAM) of the 64QAM-demodulated data is calculated, and it is determined whether the error rate E(64QAM) is less than the threshold level Eth2(at V11). That is, the slaves3A to3Z determine whether to receive the 64QAM-modulated data. Each slave3A to3Z transmits ACK64QAM(k) (k=1 to Z) to the master2at V12when the condition at V11is satisfied.

In contrast, when it is determined that the error rate E(64QAM) is less than the threshold level Eth2at V11, the number of matching times m3 is counted, and the process branches depending on this counting result. For example, it is determined whether the number of matching times m3 is equal to or greater than a predetermined number of times M3 (at V14).

Like the above-mentioned, the number of matching times m3 signifies the number of times the communication matching circuit3eperforms the matching process with the aperture antenna3idepending on control by the control circuit3a. The control circuit3astores this number of matching times m3. When the 64QAM modulation and demodulation type is selected, the error rate may be high. In such a case, the matching process is performed by the communication matching circuit3e(at V15). When the capacity value of the variable capacity capacitor3kis adjusted step by step, the error rate E of the data received by the slave3A to3Z may be made low.

Thus, when the error rate E(64QAM) becomes less than the predetermined threshold level Eth2in response to the matching process at V15by the communication matching circuit3e(V11: YES), the slaves3A to3Z transmit ACK64QAM(k) to the master2at V12. This case selects 64QAM as a communication phase at V13, permitting the present system1to have the greatest data rate.

In contrast, when the error rate E(64QAM) remains not less than the predetermined threshold level Eth2regardless of equal to or greater than a predetermined number of matching times M3 (V14: YES), the communication phase selects 16QAM in order to decrease the number of communications data per symbol by one step at V16. Then, the modulation and demodulation type adjustment mode is ended.

As illustrated inFIG. 9, when the master2receives ACK64QAM(k) (k=1 to Z) from all the slaves3A to3Z (U8: YES), the master2selects 64QAM as a communication phase (at U9), and ends the modulation and demodulation type adjustment mode.

However, when any one of the slaves3A to3Z does not transmit ACK64QAM(k), the master2naturally does not receive ACK64QAM(k) from all the slaves3A to3Z. At this time, the master2selects 16QAM as a communication phase (at U10), and ends the modulation and demodulation type adjustment mode. In this case, the master2notifies all the slaves3A to3Z that 16QAM is selected as a communication phase.

Thus, the master2and the slaves3A to3Z adjust the modulation and demodulation type. The above procedure or processes are undergone to determine the communication frequency and the modulation and demodulation type.

FIG. 11andFIG. 12illustrate BER (Bit Error Rate) versus SNR (Signal to Noise Ratio) of communication types for explaining the communication frequency adjustment mode and modulation and demodulation type adjustment mode.

As illustrated inFIG. 11andFIG. 12, SNR of the carrier can be increased based on the adjustment of the communication frequency according to the property control of the matching circuit2eand the communication matching circuit3e, or the communication frequency control of the modulation and demodulation circuit2c. With the increase of SNR, the BER decreases. When selecting a modulation and demodulation type having a greater assignment bit number per symbol, the BER tends to become higher on a condition that SNR is similar.

As explained above, in the communication frequency adjustment mode, the error rate is made equal to or less than the threshold level Eth1when the BPSK modulation and demodulation type is applied. Therefore, as illustrated inFIG. 11, the communication frequency, which corresponds to SNR: P2, is adjusted to satisfy the condition that the error rate is less than the threshold level Eth1when the BPSK modulation and demodulation type is applied.

In addition, in the modulation and demodulation type adjustment mode, the modulation and demodulation mode is selected to satisfy the condition that the error rate is less than the threshold level Eth2(≧Eth1). Therefore, as illustrated inFIG. 12, the modulation and demodulation type is changed in order of BPSK→QPSK→16QAM→64QAM. When the modulation and demodulation type is changed in this predetermined order, the number of assignment bits per symbol increases in the predetermined order, increasing the data rate as illustrated inFIG. 13. As illustrated inFIG. 12, even when SNR is unchanged at this time, the error rate increases in the predetermined order. In the example illustrated inFIG. 12, when selecting a modulation and demodulation type satisfying the condition that the error rate is less than the threshold level Eth2, the 16QAM type is selected.

Features of First Embodiment

In the present embodiment, an opening area in between the twisted portions4A to4B of the twisted wires4faces an opening area of the aperture antenna3hof the slave3A to3Z; thus, electric power can be distributed using the twisted wire4. The master2A can transmit a data modulation signal while receiving a reply signal. Further, the use of the pair of twisted wires4decreases leakage magnetic flux. Thereby, the electric power and the data modulation signal can be propagated efficiently; the contactless power line communication can be performed efficiently between the master2and slaves3A to3Z.

The master2may divide or distribute the electric power and the data modulation signal into the slaves3A to3Z. Dividing does not need other components such as a harness and a connector. In addition, each slave3A to3Z contains an error rate monitor circuit3gto measure an error rate, and ends a communication frequency adjustment mode on a condition that the measurement result of the error rate is less than the predetermined threshold level Eth1.

In contrast, when the error rate becomes equal to or greater than the predetermined threshold level, the matching circuit3eof the slave3A performs a matching process. Thereby, the data communication between the master2and the slaves3A to3Z may be made with high quality and high speed.

Even when performing a matching process, the slaves3A to3Z may not transmit ACKBPSK(k). In such a case, the master2naturally does not receive any ACKBPSK(k). At this time, the master2changes the carrier communication frequency of the modulation and demodulation circuit2c. Changing the communication frequency of the modulation and demodulation circuit2cmakes the communication between the master2and the slaves3A to3Z favorable.

In addition, in the modulation and demodulation type adjustment mode, BPSK is changed into other modulation and demodulation types such as QPSK, 16QAM, and 64QAM having higher data rates than BPSK one by one; the slaves3A to3Z perform matching processes.

The slaves3A to3Z repeat matching processes using the communication matching circuit3euntil the number of matching times m1, m2, m3 reaches predetermined number of times M1, M2, M3. In contrast, the slaves3A to3Z ends the matching process when the number of matching times m1, m2, m3 reaches the predetermined number of times M1, M2, M3 while selecting another modulation and demodulation type having a smaller number of assignment data per symbol by one step than the present type, thereby performing a usual power line communication process.

That is, when the error rate in the QPSK modulation and demodulation type becomes equal to or greater than the threshold level Eth2, the usual power line communication is started by selecting the BPSK communication phase having a smaller number of assignment data per symbol by one step than the QPSK communication phase.

Further, when the error rate in the QPSK modulation and demodulation type becomes less than the threshold level Eth2and then the error rate in the 16QAM modulation and demodulation type becomes equal to or greater than the threshold level Eth2, the usual power line communication is started by selecting the QPSK communication phase having a smaller number of assignment data per symbol by one step than the 16QAM communication phase.

Further, when the error rate in the 16QAM modulation and demodulation type becomes less than the threshold level Eth2and then the error rate in the 64QAM modulation and demodulation type becomes equal to or greater than the threshold level Eth2, the usual power line communication is started by selecting the 16QAM communication phase having a smaller number of assignment data per symbol by one step than the 64QAM communication phase. This permits the communication between the master2and the slaves3A to3Z to select a suitable modulation and demodulation type, enabling the data communication to be of a higher quality and a higher speed.

Second Embodiment

FIG. 14illustrates a second embodiment, which has differences from the first embodiment in that any control of impedance matching using the matching circuit2eand the communication matching circuit3eis not performed while only a control of communication frequency of the modulation and demodulation circuit is performed. Portions identical to those in the first embodiment are assigned with the reference signs identical to those in the first embodiment and omitted from the explanation; the different portions are only explained on a priority basis.

The following will explain portions ofFIG. 14different fromFIG. 1. The control circuit2adoes not connect a control line to the matching circuit2e. The control circuit2aconnects a control line to the modulation and demodulation circuit2c, controlling only the communication frequency of the modulation and demodulation circuit2c. The matching circuit2eof the master2contains a fixed capacity capacitor which replaces a variable capacity capacitor2hof the first embodiment. This configuration permits the matching circuit2eto match a pair of twisted wires4having a loop shape under a predetermined impedance, precluding an impedance adjustment according to control of the control circuit2a.

Similarly in the slave3A to3Z, the communication matching circuit3eis equipped with a fixed capacity capacitor which replaces the variable capacity capacitor3kof the first embodiment. Therefore, the communication matching circuit3ematches with the aperture antenna3iunder a predetermined impedance, precluding an impedance adjustment according to control of the control circuit3a.

This configuration eliminates the process at T6inFIG. 8in the communication frequency adjustment mode. That is, the slaves3A to3Z determines whether the error rate E(BPSK) is equal to or less than the predetermined threshold Eth1, whereas the master2changes a communication frequency of the modulation and demodulation circuit2cwhen exceeding the predetermined threshold level Eth1. Thereby, the communication frequency may be changed between master2and the slaves3A to3Z.

In addition, the above configuration eliminates the processes at V3, V4, V8, V9, V14, and V15inFIG. 10in the modulation and demodulation type adjustment mode. While any matching process is not performed in all the slaves3A to3Z, a usual power line communication may be started by using a modulation and demodulation type satisfying a condition that the corresponding error rate E(QPSK), E(16QAM), or E(64QAM) is less than the predetermined level Eth2.

In addition, the above configuration does not need a control line between the control circuit2aand the matching circuit2eand a control line between the control circuit3aand the communication matching circuit3e, as compared with the first embodiment, thereby simplifying the component circuit.

Third Embodiment

FIG. 15toFIG. 17illustrate a third embodiment, which has differences from the first embodiment in that at least one of the communication frequency control and the modulation and demodulation type control is excluded while controlling the characteristics of the matching circuit2eand the communication matching circuit3e. Portions identical to those in the first embodiment are assigned with the reference signs identical to those in the first embodiment and omitted from the explanation; the different portions are only explained on a priority basis.

The following will explain portions ofFIG. 15different fromFIG. 1. The control circuit2aof the master2does not connect a control line to the modulation and demodulation circuit2c. In addition, the control circuit3aof each slave3A to3Z does not connect a control line to the modulation and demodulation circuit3c. The control circuit2acontrols a matching characteristic of the matching circuit2e; the control circuit3acan control a matching characteristic of the communication matching circuit3e. In the adjustment mode, the process in the communication frequency adjustment mode illustrated inFIG. 7andFIG. 8is performed, whereas the process in the modulation and demodulation type adjustment mode illustrated inFIG. 9andFIG. 10is not performed. In addition, the process at S6in the master2illustrated inFIG. 7is changed into the process which controls the matching characteristic of the matching circuit2e.

Then, the matching characteristic can be adjusted between the master2and the slaves3A to3Z like the first embodiment, permitting a favorable communication between the master2and the slaves3A to3Z. The above configuration does not need a control line between the control circuit2aand the modulation and demodulation circuit2cand a control line between the control circuit3aand the modulation and demodulation circuit3c, as compared with the first embodiment, thereby simplifying the component circuit.

In addition, as illustrated inFIG. 16, although the communication frequencies of the modulation and demodulation circuits2cand3care controlled, whereas the modulation and demodulation type may not be controlled. In such a case, in the adjustment mode, the process in the communication frequency adjustment mode illustrated inFIG. 7andFIG. 8may be performed, whereas the process in the modulation and demodulation mode adjustment mode illustrated inFIG. 9andFIG. 10may not be performed.

In addition, as illustrated inFIG. 17, although the modulation and demodulation type controls of the modulation and demodulation circuits2cand3care controlled, whereas the communication frequency control may not be performed. In such a case, in the adjustment mode, the process in the communication frequency adjustment mode illustrated inFIG. 7andFIG. 8as well as the process in the modulation and demodulation mode adjustment mode illustrated inFIG. 9andFIG. 10may be performed. The process at S6inFIG. 7may be replaced with a matching process of the matching circuit2e.

The above configuration may control a matching characteristic of the matching circuit2eand the communication matching circuit3e, providing an effect similar to that of the first embodiment. Further, the number of control lines may be lessened, simplifying the circuit.

Fourth Embodiment

FIG. 18andFIG. 19illustrate a fourth embodiment, which has differences from the first embodiment in that while a characteristic of a matching circuit is not made by the control circuit, at least one of the communication frequency control of the modulation and demodulation circuit, and the modulation and demodulation mode control is performed. Portions identical to those in the first embodiment are assigned with the reference signs identical to those in the first embodiment and omitted from the explanation; the different portions are only explained on a priority basis.

The following will explain portions ofFIG. 18different fromFIG. 1. The control circuit2aof the master2does not connect a control line to the matching circuit2e. The control circuit3aof each slave3A to3Z does not connect a control line to the communication matching circuit3e. The matching circuit2eof the master2contains a fixed capacity capacitor which replaces a variable capacity capacitor2hof the first embodiment. This configuration permits the matching circuit2eto match a pair of twisted wires4having a loop shape under a predetermined impedance, precluding an impedance adjustment according to control of the control circuit2a.

Similarly in the slave3A to3Z, the communication matching circuit3eis equipped with a fixed capacity capacitor which replaces the variable capacity capacitor3kof the first embodiment. Therefore, the communication matching circuit3ematches with the aperture antenna3iunder a predetermined impedance, precluding an impedance adjustment according to control of the control circuit3a. The present embodiment does not perform a characteristic control of the matching circuit2eand the communication matching circuit3ewhereas performing a communication frequency control of the modulation and demodulation circuits2cand3cand a modulation and demodulation type control.

The process of the communication frequency adjustment mode illustrated inFIG. 7andFIG. 8does not perform a characteristic control of the matching circuit2eand the communication matching circuit3e. That is, the master2only performs a change control of the communication frequency at S6inFIG. 7, whereas the slaves3A to3Z performs a communication frequency control by replacing T6inFIG. 8. The process in the modulation and demodulation type adjustment mode inFIG. 9andFIG. 10is performed as explained in the first embodiment except the matching processes at V3, V4, V8, V9, V14, and V15. The favorable communication may be made between the master2and the slaves3A to3Z like the first embodiment. In addition, the above configuration does not need a control line between the control circuit2aand the matching circuit2eand a control line between the control circuit3aand the communication matching circuit3e, as compared with the first embodiment, simplifying the circuit.

Further, as illustrated inFIG. 19, although the modulation and demodulation type control of the modulation and demodulation circuits2cand3care performed, whereas the communication frequency control may not be performed. On the contrary, although the communication frequency control of the modulation and demodulation circuits2cand3cmay be performed, whereas the modulation and demodulation type control may not be performed. Even such a configuration performs at least one of the modulation and demodulation type control and the communication frequency control of the modulation and demodulation circuits2cand3c, providing an effect similar to that of the first embodiment. Further, the number of control lines may be lessened, simplifying the circuit.

Fifth Embodiment

FIG. 20illustrates a fifth embodiment, which has differences from the first embodiment in that the master2controls a power-supply frequency of the high-frequency power generation circuit (high-frequency power generation portion), whereas the slave includes a power-source monitor circuit (power-source monitor portion) of the electric power due to the power-supply frequency to perform a feedback of the power-supply frequency control. Portions identical to those in the first embodiment are assigned with the reference signs identical to those in the first embodiment and omitted from the explanation; the different portions are only explained on a priority basis.

The following will explain portions ofFIG. 20different fromFIG. 1. The control circuit (power-supply frequency control portion)2aof the master2is connected with the high-frequency power generation circuit2bvia a control line, thereby controlling the power-supply frequency of the carrier signal (high-frequency signal: power signal) which the high-frequency power generation circuit2bgenerates.

The carrier signal of the high-frequency power generation circuit2bis superimposed on the twisted wires4; the power-supply matching circuit3dreceives the carrier signal via the aperture antenna3hand outputs the power signal to the rectification circuit3f. The rectification circuit3frectifies the carrier signal, and outputs it to the power-source monitor circuit3l.

The power-source monitor circuit3lsupplies the electric power, which is rectified and smoothed by the rectification circuit3f, to the modulation and demodulation circuit3c, the error rate monitor circuit3g, the control circuit3a, and the load5A. In addition, the power source monitor circuit3lmeasures a receiving field intensity level of the carrier signal, and outputs this measurement result to the control circuit3a. The control circuit3adetermines whether the receiving field intensity level of the carrier signal is equal to or greater than a predetermined level, and performs the matching process of the power-supply matching circuit3dwhen it is determined that the receiving field intensity level is less than the predetermined level. Even when the control circuit3aof the slave3A to3Z performs the matching process of the power-supply matching circuit3dequal to or greater than the predetermined number of times, the receiving field intensity level may not become equal to or greater than a predetermined level. In such a case, the control circuit3aof the slave3A to3Z requests the master2to change the power-supply frequency.

When receiving the request of changing the power-supply frequency, the master2controls to change the power-supply frequency of the control circuit2a. Thus, the master's changing of the power-supply frequency permits the communication between the master2and the slaves3A to3Z certainly. The matching process of the power-supply frequency of the matching circuit3dmay be performed as needed.

The high quality communication processing may be achieved by subsequently performing the communication frequency adjustment mode and the modulation and demodulation type adjustment mode explained in the first embodiment. The present embodiment may achieve a high quality communication process while improve a power supply efficiency.

Sixth Embodiment

FIG. 21illustrates a sixth embodiment, which has differences from the first embodiment in that the slaves3A to3Z receives a high-frequency power with a frequency from the high-frequency power generation circuit of the master2and controls a communication frequency of the modulation and demodulation circuit. Portions identical to those in the first embodiment are assigned with the reference signs identical to those in the first embodiment and omitted from the explanation; the different portions are only explained on a priority basis.

As illustrated inFIG. 21, the slave3A to3Z includes a dividing and multiplying circuit3m. The dividing and multiplying circuit operates on direct current power which the rectification circuit3foutputs. The dividing and multiplying circuit3mis assigned with a division ratio and a multiplying ratio depending on control of the control circuit3a. The dividing and multiplying circuit3mreceives a power-supply signal via the power-supply matching circuit3d, and applies dividing or multiplying to the frequency of the power-supply signal to output to the modulation and demodulation circuit3cas a communication-use carrier.

The modulation and demodulation circuit3cof the slave3A to3Z uses the received communication-use carrier as a communication frequency for the modulation and demodulation. The modulation and demodulation circuit3cof the slave3A to3Z uses the received communication-use carrier as a communication frequency for the modulation and demodulation. This facilitates the synchronization between the master2and the slave3A to3Z. In the first embodiment, the slave3A to3Z controls a communication frequency using a high quality frequency oscillation circuit using a crystal oscillator etc. In contrast, the present embodiment need not use such a crystal oscillator etc., thereby simplifying the circuit.

Seventh Embodiment

FIG. 22illustrates a seventh embodiment, which has differences from the first embodiment in that (i) a loop coil is used while a pair of twisted wires whose ends are connected is not used and (ii) a master-side opening area of the loop coil facing a slave-side opening area of an aperture antenna is larger than another master-side opening area. Portions identical to those in the first embodiment are assigned with the reference signs identical to those in the first embodiment and omitted from the explanation; the different portions are only explained on a priority basis.

FIG. 22illustrates a configuration example of an antenna portion of the seventh embodiment. The loop coil8is composed of two core wires that are connected at their one ends to have a loop shape as being extended linearly from the main body2fof the master2in a predetermined direction (x direction). In other words, the loop coil8is provided to have no twisted portions4A to4L of the twisted wires4illustrated inFIG. 1. This loop coil8has two mater-side opening areas facing the aperture antennas3h,3ifor reception or slave3A, respectively; the opening area is in between two core wires and has a longer distance in y direction than other opening areas or gaps in between two core wires.

The main body2fof the master2transmits electric power and signals by superimposing high-frequency signals to the loop coil8. The loop coil8generates an electromagnetic field in response to the applied current. The slave3A to3Z (3B to3Z are not shown inFIG. 22) performs an electromagnetic induction connection in the electromagnetic field generated in the loop coil8using the loop-shaped aperture antennas3hand3i, thereby receiving signals (electric power and data modulation signals).

As explained above, the loop coil8has the master-side opening areas facing the reception-use aperture antennas3h,3ias gaps in between two core wires; each master-side opening area has a longer distance in a lateral direction (i.e., y direction) than other gaps in between two core wires; thus, the electromagnetic induction connection may be strengthened. In addition, as illustrated inFIG. 22, cores9such as ferrite may be provided between the master-side opening areas of the loop coil8and the aperture antennas3h,3ias needed.

The seventh embodiment provides the loop coil8composed of two core wires, which are extended from a main body of the master2and have far ends being connected to each other, for performing a power line communication. The loop coil8includes a master-side opening area as a gap in between the two core wires facing an aperture antenna; the master-side opening area is larger than other gaps in between the two core wires. This configuration strengthens an electromagnetic induction connection between the master2and the slave3A to3Z like the first embodiment.

Modifications

For example, in any one of the first to sixth embodiments, the core9explained inFIG. 22or the seventh embodiment may be provided similarly to pass through both (i) a master-side opening area of the twisted wires4in between twisted portions4A to4B,4C to4D, . . . ,4K to4L and (ii) an aperture antenna3h,3i.

The first embodiment performs two adjustment modes of the communication frequency adjustment mode and the modulation and demodulation type adjustment mode. Without need to be limited thereto, only one of the two adjustment modes may be performed.