JP2002246963A - Multiplex communication system in power line carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power line carrier multiplex communication system of high communication efficiency, for which the wastage of unused slots is reduced as much as possible, in the multiplex communication system, in which data to be communicated between a master station and a slave station connected by a power line network are mounted on time slots divided by a TDMA system, and two-way communication is performed between the master and slave stations. SOLUTION: The master station is provided with an allocation control unit 42 for setting and changing the allocating number of the time slots, corresponding to the number of the slave stations existing in the network.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power line carrier multiplex communication system for performing bidirectional communication between a master station and a slave station connected by a power line network.

[0002]

2. Description of the Related Art Power line transportation uses power distribution lines.
This is a technique for transmitting data to consumers (hereinafter, referred to as “users”) such as ordinary homes and offices. FIG. 1 is an overall schematic diagram of the power line carrier system. A low-voltage distribution line (hereinafter simply referred to as a “distribution line”) 52 is laid from the high-voltage distribution line 51 through a pole transformer 53, and a plurality of users are connected to the low-voltage distribution line. A power line network constituted by such distribution lines is called a “subnet” (in contrast, the Internet and the like are higher-level networks).

[0003] An optical / electrical converter (O / E) 55 and a PLT modem (referred to as a parent modem) 2 are connected from an upper network through an optical fiber, and the parent modem 2 and each distribution line 52 are connected. The user is connected to an information terminal device such as a personal computer through a PLT modem (called a child modem) 2. Downlink data from the upper network is transmitted through the distribution line 52 and transmitted to the information terminal device of the user. Uplink data from the information terminal device is transmitted to the upper network via the distribution line 52.

[0004]

In the power line carrier, what kind of access control system is to be adopted is a problem. However, CSMA (C
First, it is conceivable to adopt an arrier sense multiple access (Arrier Sense Multiple Access) method. However, in power line transport, reflection and attenuation due to branching of distribution lines are large, and carrier sensing may be difficult.

[0005] Thus, T
Adopting the DMA method is effective. However, T
In the DMA system, since the time allocation of slots is fixed, there are many wastes such as the occurrence of unused slots. Accordingly, it is an object of the present invention to minimize a waste of unused slots and realize a multiplex communication system in power line carrier with high communication efficiency.

[0006]

A multiplex communication system for power line carrier according to the present invention carries out two-way communication between parent and child stations on time slots divided by the TDMA system, and assigns the number of time slots to the parent station. Is provided in accordance with the number of slave stations existing in the network. According to the above configuration, since the slots are changed according to the number of slave stations, it is possible to eliminate waste of unused slots.

Although the communication capacity per slave station decreases as the number of allocated slots increases, it is desirable to set a minimum standard and limit the number of slave stations in a subnet so as to exceed this standard. It is preferable that the allocation control means sets the number of time slots allocated to be equal to the number of slave stations connected to the power line network (claim 2). Thereby, at least one slot can be allocated to one user.

[0008] Communication data from the master station to the slave station and communication data from the slave station to the master station can be transmitted and received by frequency division. This is to prevent collision of the uplink and downlink data. Thereby, the quality of communication can be improved. In the case of frequency division, it is preferable to allocate a relatively wide frequency band to communication data from the master station to the slave station and allocate a relatively narrow frequency band to communication data from the slave station to the master station. (Claim 4).
This is because generally, the transmission amount of downlink data is larger than the transmission amount of uplink data.

The frequency band assigned to communication data from the master station to the slave station or the frequency band assigned to communication data from the slave station to the master station may be variable. Thus, an optimal frequency band can be allocated according to the amount of uplink and downlink data transmission. Communication data from the master station to the slave station and communication data from the slave station to the master station may be transmitted and received by time division. This can also prevent the collision of uplink and downlink data.

A relatively wide time band may be assigned to communication data from the master station to the slave station, and a relatively narrow time band may be assigned to communication data from the slave station to the master station. 7) The time band assigned to communication data from the master station to the slave station or the time band assigned to communication data from the slave station to the master station may be variable.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OFDM (orthogonal frequency division multiple) will be described below as an example of a carrier modulation method.
An embodiment of the present invention will be described in detail with reference to the accompanying drawings, taking the case of adopting x) as an example. Since the overall outline of the power line carrier system is as described with reference to FIG. 1, the description will not be repeated.

FIG. 2 is a block diagram showing the internal configuration of a modem (common to a parent modem and a child modem). Hereinafter, the description will be made assuming a parent modem. Digital communication data transmitted from the upper network via optical fiber is
After the O / E conversion, it enters the slot assignment control unit 1 and is allocated to a time slot corresponding to the distribution destination as described later. The slot assignment control unit 1 and the modem 2 are collectively referred to as “master station”. The slot allocation control unit and the modem on the user side are collectively referred to as “slave stations”.

The data output in a time series from the slot allocation control section 1 is subjected to predetermined processing in an error correction coding circuit 3 and an interleave circuit 4 in a modem 2 and then to a serial / parallel conversion circuit. At 5, the data is parallel-converted on the frequency axis, encoded by the PSK or QAM encoding circuit 6, and changed to data on the time axis by an IFFT (inverse Fourier transform) circuit 7. The parallel / serial conversion circuit 8 converts the serial data into serial data. The guard interval insertion circuit 9 performs an operation of inserting a guard interval that brings a later symbol on the time axis.
The signal is D / A-converted by the conversion circuit 10 and converted into an analog signal.

An analog signal is modulated by a quadrature modulation circuit 11, frequency-converted (up-converted) by a mixer 12, and mounted on a distribution line (subnet). At the time of the interleave processing 4, the digital communication data is written into the buffer and read out every fixed number of bits. The fixed number of bits constitute one unit for performing the inverse Fourier transform. On the other hand, the high-frequency signal received from the distribution line is frequency-converted (down-converted) by the mixer 21, demodulated by the quadrature demodulation circuit 22, and converted into a digital signal by the A / D conversion circuit 23.

The signal converted into a digital signal is synchronized in a synchronization acquisition circuit 24, subjected to guard interval deletion processing 25, and converted into a serial / parallel conversion circuit 26.
Is converted to a parallel signal, and is Fourier-transformed on the frequency axis by the FFT circuit 27. And PSK or QA
The data is decoded by an M decoding circuit 28, converted into a serial signal by a parallel / serial conversion circuit 29, deinterleaved 30, error-corrected 31, and transmitted as digital communication data through an optical fiber.

FIG. 3 is a functional block diagram of the slot allocation control unit 1. The slot allocation control unit 1 includes a memory 41,
Control unit 42, circuit 4 for switching use area of memory 41
3, 44 are provided. The memory 41 is divided and used only for the communication setting and the number of users, and each divided portion (hereinafter referred to as “region”) of these memories corresponds to a time slot.

The control unit 42 identifies the destination of the communication data by, for example, an IP address, a MAC address, a dedicated address in a subnet, or the like, and stores the data in a memory area corresponding to the destination. At this time, the selection of the memory area is performed by controlling the switching circuit 43. The control unit sequentially sends out the data stored in each memory area to the modem under the control of the switching circuit 44. At this time, if the amount of data stored in the memory area does not fit in the time slot, only the time slot is sent, and the rest waits until the next cycle.

In the present invention, as described below, the length of the time slot per slave station is variable, so that the longer the time slot, the larger the memory area. For that slave station, the amount of data transmission per unit time increases. vice versa,
Since the memory area becomes smaller as the length of the time slot to be allocated is shorter, the data transmission amount per unit time is reduced for the slave station. Therefore, in order to secure the minimum required transmission amount, it is desirable to set an upper limit on the number of users in the subnet.

FIG. 4 is a configuration diagram of a time slot having 33 divisions. The first time slot (hereinafter simply referred to as “slot”) 1 is a downlink-only slot for broadcast notification from the master station to all slave stations. The second slot 2 is an uplink-only slot for requesting entry from the slave station to the master station. The third slot 3 is an uplink-only slot for the slave station to return acknowledgment information (ACK) to the master station in response to the allocation information.

Since the slots 1, 2, and 3 have a smaller capacity than that of data communication, the time width can be narrowed as compared with the fourth and subsequent variable allocation slots.
The fourth to 33rd slots are variable allocation slots for transmitting uplink or downlink data. The separation between uplink data and downlink data will be described later. Hereinafter, the slot assignment procedure will be described.

(1) When the number of users changes from N to N + 1 (N = 0 to 29) The master station always puts time slot delimiter marks and allocation information in slot 1 for all slave stations. Output. (2) The slave station requesting an entry puts the entry request information to the master station in slot 2. (3) The master station determines the number of assignments based on the contents of the entry request for slot 2, and outputs slot information to be assigned to the (N + 1) th user in slot 1 of the next time segment. If the entry request from the slave station does not reach the master station for some reason, the allocation information is not included in slot 1 from the master station. It is determined that the entry request has not reached the master station, and an entry request is made again.

(4) The slave station outputs an acknowledgment (ACK) with respect to the slot 1 allocation information. The master station continues to output the allocation information in slot 1 until an acknowledgment (ACK) is returned from the slave station. (5) Upon receiving confirmation (ACK) of slot 3 from the slave station, the master station adds to slot 1 that the allocation information has been determined, and outputs the result. In the above-mentioned procedures (1) to (5), since the entry request slot of the user is only one slot, when a plurality of new users request at the same time, the signals may collide and may not reach the master station. At this time, since the allocation information of slot 1 is not changed, the slave station recognizes that the entry request has not been received by the master station. However, when resending, there is a possibility that a plurality of users may collide again. By setting the waiting time (the number of waiting time segments) to be different for each user, re-collision can be avoided.

It is also considered effective to set a plurality of entry request slots in order to reduce the probability of collision. In this case, the slave station randomly determines which one of the plurality of entry request slots to use. FIG. 5 is a diagram specifically illustrating an example of time slot allocation when the number of users N is 1, 2, and 3. (a) is a diagram in which slots 4 to 33 are assigned when the number of users is 1, and (b) is a diagram in which slots 4 to 18 are assigned to one user when the number of users is 2, and other users are assigned. It is a diagram in which slots 19 to 33 are allocated, and (c) is a diagram in which, when the number of users is 3, one-third of the slots are allocated to each user. The communication speed increases as the number of slots assigned to one user increases.

Next, a method for preventing collision between uplink and downlink data in bidirectional communication will be described. In general, distribution lines have a large number of branches, and it is expected that data will collide in the upstream and downstream due to reflection at the branch point. Therefore, it is desirable to distinguish upstream and downstream data by frequency or time. Hereinafter, a method of frequency-dividing uplink and downlink data will be described. FIG. 6A shows an IFFT circuit diagram of the master station, and FIG. 6B shows an IFFT circuit diagram of the slave station. In FIG. 6A, the downlink data is assigned to a high frequency portion on the frequency axis, and in FIG. 6B, the uplink data is assigned to a low frequency portion on the frequency axis. In this way, the frequency is divided into uplink and downlink, and full-duplex communication (Frequency Division Duplex; FD)
Perform D). As a result, collision of uplink and downlink data can be prevented.

In general Internet communication, the capacity of transmission data (uplink data) from a user is smaller than the capacity of data (downlink data) received by the user. Therefore, as shown in FIG. 6, a wide band is allocated to downlink data, and a narrow band is allocated to uplink data. In addition, in the embodiment of FIG. 6, the uplink frequency band and the downlink frequency band are both fixedly assigned, but in addition to the uplink and downlink frequency bands, an uplink and downlink variable frequency band that can be assigned to any of the uplink and downlink frequency bands. It may be provided. FIG.
FIG. 3 is a diagram in which these three kinds of frequency bands are drawn in one IFFT circuit diagram.

Further, the fixed frequency band of the uplink and the downlink may be abolished, and all the frequency bands may be variable. The procedure for assigning the variable frequency band to the master station or slave station will be described. (1) The slave station sets the communication type (Web (W
WW), video conference, etc.) and send it to the master station. (2) The master station determines allocation of uplink and downlink frequency bands according to the type of communication. Specifically, in the case of WWW, the downlink data amount is much larger than the uplink data amount, so that the downlink frequency band is assigned more than the uplink frequency band.
In the case of a video conference, the amount of uplink and downlink data is almost the same, so that the downlink frequency band and the uplink frequency band are allocated to the same extent. Using the slot 1, the master station carries the frequency assignment information and transmits it down to all slave stations.

(3) The slave station changes the assignment of the input signal to the IFFT circuit based on the assignment information. As a method of performing frequency division full-duplex communication, OFDM is used.
In addition to the method of allocating an input signal to the IFFT circuit of the modulation unit, there is also a method of changing the frequency of a carrier used for uplink and downlink. The embodiments of the present invention have been described above.
The embodiment of the present invention is not limited to the above embodiment. In the above-described embodiment, different frequency bands are allocated to the time slots, so that interference in the distribution line is prevented. However, as shown in FIG. May be performed. FIG.
As shown in (1), time slots can be used alternately for every one hour segment.

[0028]

As described above, according to the multiplex communication system for power line carrier of the present invention, it is possible to realize a system with high communication efficiency by minimizing waste of unused slots.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram of a power line carrier system.

FIG. 2 is a block diagram showing an internal configuration of a modem (common to a master station and a slave station).

FIG. 3 is a functional block diagram of a slot allocation control unit 1;

FIG. 4 is a configuration diagram of a time slot having 33 divisions.

FIG. 5 is a diagram specifically showing an example of time slot allocation when the number of users N is 1, 2, and 3.

FIG. 6 (a) is an IFFT circuit diagram of a master station, and FIG. 6 (b) is a IFFT circuit diagram of a slave station.

FIG. 7 is an IFFT circuit diagram in which three types of frequency bands are drawn into one.

FIG. 8 is a time slot allocation diagram in a case where full-duplex communication is performed by time division in uplink and downlink.

FIG. 9 is a time slot diagram in a case where time slots are used alternately in uplink and downlink for each time segment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Slot allocation control part 2 Modem 3 Error correction coding circuit 4 Interleave circuit 5 Serial / parallel conversion circuit 6 PSK or QAM coding circuit 7 IFFT (inverse Fourier transform) circuit 8 Parallel / serial conversion circuit 9 Guard interval insertion circuit 10 D / A conversion circuit 11 Quadrature modulation circuit 12 Mixer 21 Mixer 22 Quadrature demodulation circuit 2 A / D conversion circuit 24 Synchronization acquisition circuit 25 Guard interval deletion circuit 26 Serial / parallel conversion circuit 27 FFT circuit 28 PSK or QAM decoding circuit 29 Parallel / Serial conversion circuit 30 Deinterleave circuit 31 Error correction circuit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasunori Abe 4-1 Egasaki-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside the System Research Laboratories of Tokyo Electric Power Company (72) Inventor Masashi Kuwahara 4th Egasaki-cho, Tsurumi-ku, Yokohama-shi, Kanagawa No. 1 Tokyo Electric Power Company System Research Laboratory F-term (reference) 5K028 AA11 DD01 DD02 HH00 KK03 KK12 LL12 RR02 5K046 AA03 BA00 BB05 PP03 PP04 PP06 PS02 PS33

Claims (8)

[Claims] 1. A multiplex communication system in which data to be communicated between a master station and a slave station connected by a power line network is placed in a time slot divided by a TDMA system and two-way communication is performed between the master and slave stations. A multiplex communication system for power line carrier, characterized in that the master station is provided with an allocation control means for changing the number of time slots allocated according to the number of child stations existing in the network. 2. The multiplex communication system according to claim 1, wherein said allocation control means sets the number of allocated time slots to be equal to the number of slave stations connected to the power line network. 3. The multiplex communication system according to claim 1, wherein communication data from the master station to the slave station and communication data from the slave station to the master station are transmitted and received by frequency division. 4. A relatively wide frequency band is allocated to communication data from the master station to the slave station, and a relatively narrow frequency band is allocated to communication data from the slave station to the master station. The multiplex communication system for power line carrier according to claim 3. 5. The frequency band assigned to communication data from a master station to a slave station or the frequency band assigned to communication data from a slave station to a master station is made variable. Multiplex communication system in power line carrier. 6. The multiplex communication system according to claim 1, wherein communication data from the master station to the slave station and communication data from the slave station to the master station are transmitted and received by time division. 7. A relatively wide time band is assigned to communication data from the master station to the slave station, and a relatively narrow time band is assigned to communication data from the slave station to the master station. The multiplex communication system for power line carrier according to claim 6. 8. The time band assigned to communication data from the master station to the slave station or the time band assigned to communication data from the slave station to the master station is variable. Multiplex communication system in power line carrier.