JP3556145B2 - Power line data transmission system - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement in a power line data transmission system for transmitting meter reading data and other data using a power line such as a distribution line as a signal transmission path.
[0002]
[Prior art]
A power line has much noise generated by a load connected to the power line, and also has a large attenuation in a high frequency band used for signal transmission due to the influence of the load. For this reason, power lines are not good transmission lines, but the use of already wired power lines has the advantage that there is no need to lay new signal transmission lines. , Such as ON / OFF control of contacts, which can be used even when the transmission speed is low.
[0003]
When data transmission is performed, a dedicated line such as a coaxial cable or an optical cable is generally used as a transmission line. As a representative data transmission method, there is a LAN conforming to IEEE802.3, and in this LAN, transmission control is performed by a CSMA / CD (Carrier Sense Multiple Access / Collision Detection) method. The transmission device, which has received the data to be transmitted from the information device, performs transmission if it confirms that no carrier exists on the transmission path. Monitors the transmission line voltage during transmission, and if the voltage is out of the specified range, determines that it has collided with another transmission, stops transmission, and waits for the time generated by random numbers. And then resend. Other transmission devices on the transmission path normally receive the data on the transmission path, and when the data is addressed to its own address or the broadcast address, transfer the data to the information device. An IEEE 802.3 compliant LAN maintains transmission line characteristics that enable high-speed transmission by regulating the transmission speed, line length, and the number of transmission devices depending on the type of dedicated line used, so that there is no collision in transmission. In other words, it is assumed that the data is correctly transmitted to the other party, and does not require a reception response from the other party.
[0004]
In recent years, information devices such as personal computers have become widespread not only in offices but also in homes, and various local area networks have been actively constructed. Under such circumstances, attention has been paid to power line carriers that can transmit signals without wires, and local area networks using power line carriers are being studied.
[0005]
In power line carrier, transmission line characteristics must be improved in order to perform high-speed transmission corresponding to information equipment, but the commercial power frequency is passed between the load connected to the power line and the power line transmission line, and the high-frequency signal is transmitted. It is known that transmission characteristics can be improved by inserting a blocking filter (FIG. 19) for attenuating band signals. In FIG. 19, L1 and L2 are coils, and C1 is a capacitor.
[0006]
That is, by inserting a blocking filter into a load that significantly deteriorates the transmission path characteristics, high-speed transmission by power line carrier becomes possible. According to the current Radio Law, a band of 10 kHz to 450 kHz can be used, and the transmission speed is not limited as long as it is used in a range separated from other power lines by a blocking filter. To reduce the size of the blocking filter, transmission of 100 kbps or more is possible even if the band used is limited to 200 kHz or more.
[0007]
[Problems to be solved by the invention]
However, when performing data transmission, it is necessary to employ not only high-speed signal transmission but also transmission control corresponding to data transmission. In a LAN conforming to IEEE802.3, which is a typical data transmission method, transmission control is performed according to the CSMA / CD method. However, in a power line carrier, since a signal is greatly attenuated, is a carrier present on a transmission path? Although it can be determined whether it is possible, it is difficult to detect a collision. In addition, even if the load does not normally generate noise, noise that has a significant effect on the transmission line can be generated instantaneously when the power is turned on / off or when the operation mode is switched. Since it is not practical to insert a blocking filter into the load, it is necessary to perform retransmission control based on the presence or absence of a reception response from the transmission destination in order to ensure reliability suitable for data transmission. In power line carrier with large signal attenuation, the preamble preceding the head and data of the transmission signal must be longer than the preamble of the baseband transmission by the dedicated line for gain control, etc. If necessary, there is a problem that the data transmission throughput is significantly reduced. In the case of a broadcast address, there is another problem that it is more difficult to confirm a reception response in a short time.
[0008]
(Object of the invention)
An object of the present invention is to provide a power line data transmission system capable of solving the above-mentioned problems and constructing a highly reliable local area network suitable for data transmission by power line carrier.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a power line data transmission system that uses a power line as a signal transmission line and performs data transmission between a plurality of power line carrier devices connected to the power line. The transmission phase cycle to be determined, a plurality of specific phases different in the transmission phase cycle are respectively assigned to the plurality of power line carrier devices as a transmission start phase,When the power line carrier has two transmission phases and the next transmission phase 1 If it detects that there is no carrier on the transmission path by the transmission start phase assigned to itself in the cycle,Start transmitting a message from the transmission start phase assigned to itselfThen, between the first and last transmission start phase in the transmission phase cycle from the next transmission start phase to the next, so as not to end the transmission, as a reception response when the self-addressed message is received normally, the power line carrier device And transmitting a carrier from the transmission start phase assigned to itself in the next transmission phase cycle after receiving the message addressed to itself.It is characterized by doing so.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an example of a local network according to the present invention. Transmission lines 3 and 4 denote ranges divided by the power line blocking filter 1 or the power transformer 2, and the power line carriers 5a to 5g and the power line carriers 5a to 5c and 5d connected to the transmission lines 3 and 4, respectively. Information devices (personal computers) 6a to 6c and 6d to 6g which exchange data through .about.5g constitute a local area network 7 by the transmission path 3 and a local area network 8 by the transmission path 4.
[0013]
The power line carriers 5a to 5g transmit data using power lines in response to data transmission requests from the information devices 6a to 6g. The number of power line carriers connected to one transmission line 3 or 4 is limited in advance. Here, a description will be given assuming that the limited number is 30. Each of the different 0, 1, 2,..., 28, 29 addresses is set for the power line carrier used. Then, as shown in FIG. 2, a half wavelength (both positive and negative) of the power line voltage wave 9 is set as one transmission phase cycle, and as shown in FIG. The transmission phase is assumed to be the transmission phase of the power line carrier having addresses 0 to 29 at equal intervals of 6 degrees. That is, since address × 6 degrees = transmission start phase, for example, the transmission start phase of the power line carrier having address 4 is 24 degrees. In the case of the power frequency of 50 Hz, the time is 1.333 ms from the zero cross, and in the case of the power frequency of 60 Hz, the time is 1.111 ms from the zero cross. Note that one cycle of the transmission phase can be set to 1 / integer multiple of a half wavelength of the power line voltage wave 9.
[0014]
Here, a case is considered in which the power line carrier having the address 4 transmits a message to the power line carrier having the address 25. The power line carrier having the address 4 must have no carrier on the transmission line by two cycles of the transmission phase (one cycle of the power line voltage wave 9) and the transmission start phase 24 degrees corresponding to the own address in the next one phase of the transmission phase. Then, as shown in FIG. 4, the transmission of transmission data of the transmission data is started from a transmission start phase of 24 degrees. Even after transmitting the message, the transmission is terminated by controlling the carrier wave output so that the transmission is not terminated between 0 and 6 degrees and 174 and 180 degrees in the transmission phase cycle. The power line carrier on the receiving side having the address 25 receives, as a reception response when the message is normally received, an adjacent transmission start phase corresponding to its own address in the next transmission phase cycle in which the reception of the message has been completed, from 150 degrees. A carrier is transmitted as a reception response signal until the next transmission start phase of 156 degrees. When the power line carrier having the address 4 detects a carrier on the transmission line between 150 degrees and 156 degrees, it recognizes that the power line carrier having the address 25 has received the message normally. Since the reception response can be confirmed by receiving only the carrier wave, the reception can be confirmed in a short time.
[0015]
The structure of the message includes, for example, a header section, a data section, and an error detection section as shown in FIG. 5, and the header section includes a source address, a destination address, and the like. The power line carrier device that has received the message transmits a carrier wave as a reception response signal when the transmission destination address is its own address or a broadcast address.
[0016]
If the power line carrier having the address 4 cannot detect a carrier (reception response signal) on the transmission path between 150 degrees and 156 degrees in the next transmission phase cycle after the transmission of the message, the transmission phase cycle ends. Without waiting for two transmission phase cycles, the same message is retransmitted from the transmission start phase 24 degrees corresponding to the own address in the next transmission phase cycle of the transmission phase cycle for which no response was confirmed, and if there is no response, The retransmission may be performed a preset number of times.
[0017]
The power line carrier having the address 4 can detect the carrier on the transmission line between 150 degrees and 156 degrees in the next transmission phase cycle of the transmission phase cycle after the completion of the message transmission, and the power line carrier having the address 25 can be detected. If there is data to be transmitted after the transmission phase, the transmission start phase corresponding to the own address in the next transmission phase cycle after the transmission phase cycle in which the reception response has been confirmed can be set in advance without waiting for two transmission phase cycles. The continuous transmission of a different message may be performed by the number of times performed.
[0018]
When transmitting to the power line carrier having the address 25 or another address after transmitting the power line carrier having the address 4 continuously for the preset number of times, the transmission phase is three cycles or more and the next transmission phase. It detects that there is no carrier on the transmission line by the transmission start phase corresponding to the own address in one cycle, and starts message transmission from the transmission start phase 24 degrees corresponding to the own address.
[0019]
The transmission control is performed as described above. However, it is the transmission phase 1 cycle that detects that there is no carrier in the transmission phase 2 cycle when transmitting first except for the case of retransmission or continuous transmission. This is because, when there is no reception response, transmission is performed to another power line carrier having a higher transmission start priority, so that retransmission cannot be continuously performed.
[0020]
The transmission end prohibition section is defined as 0 to 6 degrees and 174 to 180 degrees in the transmission phase cycle. When a message is terminated between 0 to 6 degrees, it is unclear which transmission phase cycle has been completed on the receiving side. This is because, when the message is terminated between 174 and 180 degrees, the power line carrier having the transmission start phase of 0 degrees may fail to respond. Further, when performing transmission after performing a predetermined number of continuous transmissions, detecting that there is no carrier in the transmission phase of 3 cycles or more is performed by positioning the transmission priority at the lowest position. This is to prevent a power line carrier having a low transmission rate from being unable to transmit.
[0021]
The data transmission method of specifying a destination has been described above. However, the same method as that of the above-described data transmission method may be applied to data transmission to a broadcast address for transmitting data to all connected power line carriers. Even if the reception response signals are returned from all the power line carriers during one cycle of the transmission phase in which the reception response is expected, since they are located at different phases, there is no collision. Even in broadcast transmission, reception can be confirmed in a short time.
[0022]
However, if the power line carrier on the transmitting side does not know what power line carrier is connected on the transmission path, retransmission control cannot be performed. Therefore, each power line carrier holds a connection list in which connectable power line carriers are registered. For example, if there are four power line carriers having addresses 6, 11, 20, and 27 in one local area network, and the power line carrier at address 6 transmits a message addressed to a broadcast address, as shown in FIG. As described above, there is a reception response from the power line carrier at addresses 11, 20, and 27, but of course, there is no reception response signal at the phase corresponding to the other addresses. As a result, the power line carrier at address 6 confirms the other connected power line carrier, and creates and holds a connection list.
[0023]
FIG. 7A shows a basic connection list in the case of the above example. It is better that the connection list is automatically created in order to flexibly cope with addition and deletion. The connection list automatic creation method is a method in which a connection confirmation message addressed to a broadcast address is transmitted when the power line carrier is started, and the connection list is automatically registered in response to the reception response. In this case, the data portion of the message to be transmitted may be empty. Also, at a preset time interval, a connection confirmation message addressed to the broadcast address is transmitted, and the connection list is automatically registered and updated based on the reception response. When there is no registration in the connection list, the automatic registration of the connection list may be repeatedly performed. Also, in the data transmission / reception of data transmission, if a message from a power line carrier that is not registered in the connection list is normally received, the power line carrier is registered in the connection list, and retransmission is performed a preset number of times. If the received response after the transmission of the message cannot be confirmed even after retransmission, the unresponsive power line carrier is deleted from the connection list. By these operations, the state of the power line carrier connected to the transmission path can be kept up to date. In addition, as shown in FIG. 7B, the connection list is advantageously weighted according to the presence or absence of a response.
[0024]
When the power line carrier starts up, the connection list is automatically registered.If a carrier is detected at the transmission start phase corresponding to the own address as a reception response at that time, a display notifying the abnormality is displayed. Stopping the function can prevent confusion in the system due to address duplication.
[0025]
When transmitting a large amount of data, retransmission control becomes more efficient if a plurality of packets are transmitted collectively and a reception response is returned for each packet, instead of increasing the amount of data transmitted at one time. Even in the case of the present invention, if the number of devices to be used (integer) is limited to M / N (M: maximum number of connected devices, N: number of packets), N packets can be transmitted at one time. Consider a case in which a maximum of 30 devices can be connected and only 4 devices are used. The number N of packets at this time is 7. The addresses of the four power line carriers to be used are set to 0, 7, 14, 21. It is also set that the number of used power line carriers is limited to four. This makes it possible to transmit seven packets at once.
[0026]
Here, as shown in FIG. 8, a case is considered where the power line carrier having the address 7 transmits a message to the power line carrier having the address 21. The power line carrier having the address 7 starts transmission after detecting that there is no carrier on the transmission path by the transmission start phase 42 degrees corresponding to the own address in the transmission phase 2 cycles or more and the next transmission phase 1 cycle. From the phase, transmission of a message consisting of seven packets starts. Even after sending the message, the transmission is terminated by controlling the carrier wave output so as not to terminate the transmission between 0 and 6 degrees and 174 and 180 degrees in the transmission phase cycle. The power line carrier having the receiving side address 21 transmits a signal of the received message when the reception status of the plurality of seven packets is ×× ○ ×× ○ (○ is normal reception, X is abnormal reception). From the transmission start phase 126 ° corresponding to the own address in the next transmission phase cycle after the transmission phase cycle in which has been completed, the carrier is ××× ○ ○ (○ is transmitted in seven phase sections at intervals of 6 °) , × are not transmitted). Thus, the power line carrier having the address 7 can recognize the reception status of each packet of the power line carrier having the address 21. This method of simultaneously transmitting a plurality of packets is also effective for a message addressed to a broadcast address.
[0027]
As shown in FIG. 9, each power line carrier device includes a power line coupling circuit 11 connected to a power line via a power line connection terminal 10, a transmission phase detection circuit 12 for detecting a phase in a transmission phase cycle, and a carrier wave on a transmission path. A carrier detection circuit 13 for detecting the presence / absence, a signal transmission control circuit 14 for transmitting a transmission data signal, a connection confirmation signal, a reception response signal, etc., an output amplification circuit 15, a gain control circuit 16 for changing the level of the received carrier, A carrier unit 18 including a signal modulation / demodulation circuit 17 for modulating a carrier wave to be transmitted and demodulating a received signal, a control unit 19 such as a CPU, and an external device connected to an information device (FIG. 1) via an external connection terminal 20. It comprises an interface unit 21, a display unit 22, a setting unit 23, a timer 24, a memory 25, and a power supply unit 26. The display unit 22 is configured by an LED or the like, and displays a status such as transmitting or receiving, an abnormal status such as no connection list registration, address duplication, and other displays. The setting unit 23 includes a manual switch for setting an address and the like. The timer 24 has a function of notifying the control unit 19 of the automatic update time of the connection list and the like. The memory 25 stores its own address, connection list, data, and the like.
[0028]
As transmission control, a carrier can be detected in one transmission start phase section (for example, a phase of 0 to 6 degrees in the case of address 0), and a carrier can be transmitted in one transmission start phase section. Since it is indispensable, the power line carrier device can not only transmit and receive signals for high-speed transmission, but also transmit and receive amplitude modulated signals using the same carrier and having a modulation section equal to one transmission start phase section. it can. This amplitude modulation signal may be used as a communication means such as a backup at the time of retransmission. For example, when a half wavelength of the power line voltage wave 9 is set as one transmission phase cycle and each transmission start phase section obtained by dividing the half cycle is assigned to the power line carrier device of the address 0 to 29, it is equal to the transmission start phase section. Transmission and reception of an ASK signal having a modulation section of a length can be realized without adding anything to the device. That is, in FIG. 9, a carrier is modulated by turning on / off a switch of the signal transmission control circuit 14 in accordance with data to be transmitted to generate an ASK signal, which is injected into a power line. When receiving, the signal is demodulated by the carrier detection circuit 13. For example, when transmitting a message by the ASK signal from the power line carrier at address 8 to the power line carrier at address 20, the result is as shown in FIG. The data transmission according to the present invention described above with reference to FIG. 4 is performed at a transmission speed of 100 kbps or more by, for example, a PSK signal, while the data transmission according to the ASK signal described with reference to FIG. If a half wavelength is divided into 30, the transmission speed becomes 3 kbps. When priority is given to reliability over speed, data transmission is performed using an ASK signal of 3 kbps. Note that the modulation section of the ASK signal may be an integral multiple of the transmission start phase section. In that case, the transmission speed is 1 / integer multiple of 3 kbps.
[0029]
As a system configuration, there are cases where it is desired to treat different transmission paths as the same area network. That is, a general power line is wired with a single-phase three-wire outdoors and divided into a red phase and a black phase indoors, and it is desired to treat the indoor red phase and black phase as the same area network. Alternatively, when all the power line carriers cannot communicate with each other when the transmission path is long, if the transmission path is separated by using a blocking filter, it is desired to treat these transmission paths as the same area network.
[0030]
For example, as shown in FIG. 11, the black lines of the single-phase three-wire indoor wiring separated from the outdoor wiring by the blocking filter 1 are connected to the power line carriers at addresses 1, 4, and 9, and the red phase is addressed to the address 14. , 20, and 27, the communication cannot be performed between the power line carriers having different phases. (The actual signal leaks to other phases, but is not suitable for practical use because it is extremely attenuated.) In such a case, the transport unit 18a connected to the black phase and the transport unit connected to the red phase A power line carrier bridge device 27 that has an address 18b and a control unit 19, has one address (for example, 11), a connection list of black phase and red phase, and transfers signals between different phases is used.
[0031]
Further, as shown in FIG. 12, when the indoor wiring is long, the signal is greatly attenuated, and when the power line carrier at address 1 and the power line carrier at address 27 cannot communicate stably, the communication can be performed reliably. In order to secure an area, a transmission path may be divided by inserting a blocking filter 1b inevitably. In such a case, the power line carrier bridge device 27 is used to connect the transport units 18a and 18b to the indoor wiring on both sides of the blocking filter 1b.
[0032]
If the message received from a certain transmission line is a message addressed to a power line carrier registered in a connection list of another transmission line, the power line carrier bridge device 27 sends a reception response instead of the power line carrier. Then, the message is transmitted to the target transmission line. If the message received from one transmission line is a message addressed to a broadcast address, a reception response is performed in place of all the power line carriers registered in the connection list of another transmission line, and the broadcast address is addressed. Send the message to another transmission path. Also, in order to prevent transmission from being repeated in a loop between different transmission paths, a message addressed to the broadcast address is not transmitted to the transmission path to which the power line carrier of the source address is connected. In addition, in order to simplify transmission control, the number of power line carrier bridge devices 27 that directly connect a certain transmission line to another transmission line is limited to one.
[0033]
As is apparent from FIGS. 11 and 12, the power line carrier device 27 is used together with the blocking filter. Therefore, the integrated structure makes it possible to reduce the size and facilitate handling. 13 shows a device 28 in which the power line carrier bridge device 27 of FIG. 11 is integrated with the blocking filter 1, and FIG. 14 shows a device 29 in which the power line carrier bridge device 27 of FIG. 12 is integrated with the blocking filter 1b. ing.
[0034]
On the other hand, there are cases where it is desired to connect different local area networks. For example, connections between local area networks separated by a blocking filter for each indoor floor, or connections between indoor and outdoor local area networks, or more than the maximum number of power line carriers connected on a transmission path Sometimes, a connection between local area networks when a transmission path is divided by using a blocking filter is used. In such a case, it has a plurality of addresses corresponding to a plurality of different local area networks, and a connection list of each different local area network, checks the data content in the message, and satisfies a predetermined condition. In such a case, a power line carrier router device for transferring a signal between local networks is used. This power line carrier router device 30 is shown in FIG. The configuration is the same as that of the power line carrier bridge device 27, except that the address 12 of the local network A is assigned to the transport unit 18a, and the address 3 of the local network B is assigned to the transport unit 18b, and the message configuration is different. The message structure is as shown in FIG.
[0035]
Consider a case where the power line carrier at address 5 of the local area network A transmits a message to the power line carrier at address 5 of the local area network B. The transmission destination address of the header part of the message is the address 12 of the carrier 18a of the power line carrier router device 30, the flag of the data part of the message is 1 (set) meaning transfer to a different local area network B, and The source address is 5, which is the same as the source address in the header, and the destination address is the address 5 of the power line carrier of the local area network B. Therefore, if the flag in the data portion of the received message is 1, the power line carrier router device 30 transfers the received message to the power line carrier at the destination address 5 as it is.
[0036]
Since the power line carrier router device 30 is used together with the blocking filter in the same manner as the power line carrier bridge device 27, it is easier to handle the power line carrier device 30 while reducing the size and integrating the device.
[0037]
As a form in which different local area networks are connected and used, there is a case where outdoor wiring and indoor wiring are connected as shown in FIG. (Because the outdoor wiring belongs to the power company and the indoor wiring belongs to the customer, it is better to manage them as different local area networks.) In FIG. 17, PC is an information device, PLC is a power line carrier, BF is a blocking filter, and RT is a blocking filter. The power line carrier router device, WHM, is a watt hour meter. The local area network within the customer is connected to the local area network of the outdoor wiring by a power line carrier router (RT) for each customer A, B, and C. A power line carrier (PLC) for transmitting meter reading information of a watt hour meter (WHM) and the like is connected to a local area network of outdoor wiring. In the case of FIG. 17, since the blocking filter (BF), the power line carrier router device (RT), and the watt hour meter (WHM) are located immediately on the wiring, they are integrated into one structure as shown in FIG. If the device 31 is used, the installation space is reduced and it is easy to handle, and the power line carrier router device (RT) can transmit the meter reading information of the watt hour meter (WHM).
[0038]
【The invention's effect】
As explained above,The present inventionAccording toTwo transmission phases and the next transmission phase 1 When it detects that there is no carrier on the transmission line by the transmission start phase assigned to itself in the cycle,Transmission start phaseFrom telegramSince transmission is started, random transmission avoiding collisions becomes possible, and a highly reliable local area network suitable for data transmission by power line carrier can be constructed.
[0039]
Also,The present inventionAccording toFrom the transmission start phase assigned to itself in the next transmission phase cycle after receiving the self-addressed messageSince the reception response signal of only the carrier wave is transmitted, the reception can be confirmed in a short time, and a highly reliable local area network suitable for data transmission by power line carrier can be constructed.
[Brief description of the drawings]
FIG. 1 is a diagram showing a system configuration according to an embodiment of the present invention.
FIG. 2 is a diagram showing a transmission phase cycle defined in an embodiment of the present invention.
FIG. 3 is a diagram showing a transmission start phase.
FIG. 4 is a diagram showing the relationship between transmission and reception responses when a transmission destination is specified.
FIG. 5 is a diagram showing an example of a message structure;
FIG. 6 is a diagram showing the relationship between transmission and reception responses when the broadcast is addressed.
FIG. 7 is a diagram showing an example of a connection list.
FIG. 8 is a diagram illustrating a relationship between transmission and reception response in the case of batch transmission of a plurality of packets.
FIG. 9 is a diagram illustrating an example of a circuit configuration of the power line carrier device in FIG. 1;
FIG. 10 is a diagram showing a relationship between transmission and reception response of an ASK signal which is also used for backup and the like.
FIG. 11 is a diagram showing another embodiment of the present invention when different transmission paths are treated as one local area network.
FIG. 12 is a diagram showing another embodiment of the present invention when a divided transmission path is treated as one local area network.
13 is a diagram showing a device in which the power line carrier device in FIG. 11 is integrated with a blocking filter.
14 is a diagram showing a device in which the power line carrier device in FIG. 12 is integrated with a blocking filter.
FIG. 15 is a diagram showing another embodiment of the present invention in a case where a message is transferred between different local area networks.
FIG. 16 is a diagram showing an example of a message structure used in the case of FIG. 15;
FIG. 17 is a diagram showing another embodiment of the present invention in the case where a message is transferred between a local area network with indoor wiring and a local area network with outdoor wiring.
18 is a diagram showing a device in which the power line carrier router device in FIG. 17 is integrated with a blocking filter and a watt hour meter.
FIG. 19 is a diagram illustrating a circuit configuration example of a blocking filter.
[Explanation of symbols]
1,1a, 1b blocking filter
2 Power transformer
3,4 transmission line
5a-5g Power line carrier
6a-6g Information equipment
7,8 Local area network
9 Power line voltage wave
18, 18a, 18b transport unit
19 Control part
27 Power line carrier bridge device
30 Power line carrier router device

Claims (1)

In a power line data transmission system that uses a power line as a signal transmission path and performs data transmission between a plurality of power line carrier devices connected to the power line, a transmission phase cycle synchronized with the power line voltage wave is determined. A plurality of different specific phases are respectively assigned to the plurality of power line carrier devices as a transmission start phase, and the power line carrier device has a transmission phase of two cycles and a transmission start phase assigned to itself in the next transmission phase one cycle. When it is detected that there is no carrier on the transmission path, the transmission of a message is started from the transmission start phase assigned to itself, and from the first and last transmission start phases in the transmission phase cycle to the next adjacent transmission start phase. In this case, the transmission is not terminated, and the power line carrier A power line data transmission system , wherein a transmitting apparatus transmits a carrier from the transmission start phase allocated to the transmission apparatus in a transmission phase cycle next to the reception of a message addressed to the transmission apparatus .

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