JP3808711B2 - Multiple communication system and method in power line carrier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multiplex communication system in a power line carrier that performs bidirectional communication between a master station and a slave station connected by a power line network.
[0002]
[Prior art]
Power line conveyance is a technique for transmitting data to consumers (hereinafter referred to as “users”) such as general households and offices using power distribution lines.
FIG. 1 is an overall schematic diagram of a power line carrier system. A low-voltage distribution line (hereinafter simply referred to as “distribution line”) 52 is laid from the high-voltage distribution line 51 through the pole transformer 53, and a plurality of users are connected to the ends of them. A power line network composed of such distribution lines is called a “subnet” (in contrast, the Internet or the like is a higher-order network).
[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.
A user is connected to an information terminal device such as a personal computer through a PLT modem (referred to as a child modem) 2.
Downstream data from the upper network is transmitted through the distribution line 52 and transmitted to the user's information terminal device. Uplink data from the information terminal device is transmitted to the upper network through the distribution line 52.
[0004]
[Problems to be solved by the invention]
In the power line carrier, what kind of access control method is adopted is a problem. First, it is conceivable to adopt a CSMA (Carrier Sense Multiple Access) method that is widely used in general LANs.
However, in power line conveyance, reflection and attenuation due to distribution line branching and the like are large, and carrier sense may be difficult.
[0005]
Therefore, it is effective to adopt a TDMA system in which time slots are assigned in advance. However, in the TDMA system, since the temporal allocation of slots is fixed, there is a lot of waste such as the generation of unused slots.
Accordingly, an object of the present invention is to realize a multiplex communication system and a multiplex communication method in power line carrier with high communication efficiency by minimizing waste of unused slots.
[0006]
[Means for Solving the Problems]
The multiplex communication system for power line carrier according to the present invention performs two-way communication between parent and child stations in time slots divided by the TDMA method, and sets the time slot allocation information to the number of child stations existing in the network. According to the first aspect of the present invention, there is provided an allocation control means for changing the setting accordingly.
According to the above configuration, since the slot is changed according to the number of slave stations, it is possible to eliminate the waste of unused slots.
[0007]
Although the communication capacity per slave station decreases as the number of assigned slots increases, it is desirable to provide a minimum standard and limit the number of slave stations in the subnet so as to exceed this standard.
In the multiplex communication system, if the allocation information by the allocation control means is not changed even when the slave station makes an entry request, the waiting time until the slave station makes an entry re-request to the master station is reduced. Different settings are used for each station .
The allocation control means preferably sets the number of time slot allocations in the time slot allocation information to be equal to the number of slave stations connected to the power line network (Claim 2).
As a result, one slot can be allocated to one user at a minimum.
[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 (claim 3). This is to prevent the collision of the upstream and downstream data. Thereby, the quality of communication can be improved.
When performing frequency division, it is preferable to assign a relatively wide frequency band to communication data from the master station to the slave station and assign a relatively narrow frequency band to communication data from the slave station to the master station. (Claim 4). This is because the amount of downlink data transmission is generally larger than the amount of uplink data transmission.
[0009]
The frequency band assigned to the communication data from the master station to the slave station or the frequency band assigned to the communication data from the slave station to the master station may be variable. Thereby, the optimal frequency band can be allocated according to the uplink / downlink data transmission amount.
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 (claim 6). This can also prevent collision of uplink and downlink data.
[0010]
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 (claim 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.
The multiplex communication method for power line carrier according to the present invention is a method of changing the setting of the number of time slot allocations according to the number of slave stations existing in the network. It is a method that includes procedures.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings, taking as an example a case where OFDM (orthogonal frequency division multiplex) is adopted as an example of a carrier wave modulation method.
The overall outline of the power line carrier system is as described with reference to FIG.
[0012]
FIG. 2 is a block diagram showing an internal configuration of a modem (common to a parent modem and a child modem). Hereinafter, description will be made assuming the parent modem.
The digital communication data transmitted from the host network through the optical fiber is O / E converted, then enters the slot allocation control unit 1 and is distributed to the time slot corresponding to the delivery destination, as will be described later.
The slot allocation control unit 1 and the modem 2 are collectively referred to as “master station”. Further, the slot allocation control unit and the modem on the user side are collectively referred to as “slave station”.
[0013]
The data output in time series from the slot allocation control unit 1 is subjected to predetermined processing in the error correction coding circuit 3 and interleave circuit 4 in the modem 2 and then the frequency in the serial / parallel conversion circuit 5. Parallel conversion is performed on the axis, the PSK or QAM encoding circuit 6 encodes the data, and the IFFT (inverse Fourier transform) circuit 7 changes the data to the time axis. Then, serial conversion is performed by the parallel / serial conversion circuit 8, and the guard interval insertion circuit 9 is subjected to an operation of inserting a guard interval that precedes a subsequent symbol on the time axis, and the D / A conversion circuit 10 performs D / A conversion. Converted into an analog signal.
[0014]
The analog signal is modulated by the quadrature modulation circuit 11, frequency-converted (up-converted) by the mixer 12, and mounted on the distribution line (subnet).
At the time of the interleaving process 4, the digital communication data is written into the buffer and read out every certain number of bits. This fixed number of bits is one unit for 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 orthogonal demodulation circuit 22, and converted into a digital signal by the A / D conversion circuit 23.
[0015]
The signal converted into the digital signal is synchronized in the synchronization acquisition circuit 24, subjected to guard interval deletion processing 25, converted into a parallel signal in the serial / parallel conversion circuit 26, and Fourier-transformed on the frequency axis by the FFT circuit 27. The Then, the data is decoded by the PSK or QAM decoding circuit 28, converted into a serial signal by the parallel / serial conversion circuit 29, deinterleaved 30, error corrected 31, and transmitted as digital communication data through an optical fiber.
[0016]
FIG. 3 is a functional block diagram of the slot allocation control unit 1. The slot allocation control unit 1 includes a memory 41, a control unit 42, and usage area switching circuits 43 and 44 of the memory 41.
The memory 41 is divided and used by combining the communication setting and the number of users, and each of the divided portions (hereinafter referred to as “areas”) of these memories corresponds to a time slot.
[0017]
The control unit 42 identifies the destination of the communication data by, for example, an IP address, a MAC address, a dedicated address in the subnet, and stores the data in a memory area corresponding to the destination. At this time, the memory area is selected by controlling the switching circuit 43. Further, the control unit sequentially sends 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 for the next cycle.
[0018]
In the present invention, as described below, since the length of the time slot per slave station is variable, the longer the time slot length, the larger the memory area becomes. On the other hand, the amount of data transmission per unit time increases. Conversely, the shorter the time slot to be allocated, the smaller the memory area, so that the amount of data transmission per unit time is reduced for that slave station. Therefore, in order to secure the minimum necessary transmission amount, it is desirable to set an upper limit on the number of users in the subnet.
[0019]
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 dedicated slot for broadcast notification from the master station to all the slave stations.
The second slot 2 is an uplink dedicated slot for requesting entry from the slave station to the master station.
The third slot 3 is an uplink-dedicated slot for the slave station to return confirmation information (ACK) to the master station for the allocation information.
[0020]
Since the slots 1, 2 and 3 have a smaller capacity than data communication, the time width can be narrower than that of the fourth and subsequent variable allocation slots.
The fourth to 33rd slots are variable allocation slots for sending uplink or downlink data. The separation between the uplink data and the downlink data will be described later.
The slot allocation procedure will be described below.
[0021]
(1) When the number of users is changed from N to N + 1 (N = 0 to 29)
The master station always outputs the time slot delimiter and the allocation information to all the slave stations in slot 1.
(2) The slave station requesting entry places entry request information for the master station in slot 2.
(3) The master station determines the number of allocations based on the entry request content of slot 2 and outputs the slot information allocated to the (N + 1) th user in slot 1 of the next time segment. When the entry request from the slave station does not reach the master station for some reason, the allocation information is not placed in the slot 1 from the master station. The entry request determines that the master station has not been reached and makes an entry request again.
[0022]
(4) The slave station outputs an acknowledgment (ACK) for 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 that the allocation information has been confirmed to slot 1 and outputs it.
In the procedures (1) to (5), since the user has only one entry request slot, when multiple new users request at the same time, the signals may collide and may not reach the master station. In this case, 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, if it is retransmitted, there is a possibility that multiple users may collide again. By setting different waiting times (number of waiting time segments) for each user for each user, another collision can be avoided.
[0023]
It is also considered effective to set a plurality of entry request slots in order to reduce the collision probability. In this case, the slave station randomly determines which of the plurality of entry request slots is to be used.
FIG. 5 is a diagram specifically showing 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 allocated when the number of users is 1, and (b) is a diagram in which slots 4 to 18 are allocated to one user and the other users are allocated when the number of users is 2. (C) is a diagram in which 1/3 slots are assigned to each user when the number of users is three. The greater the number of slots allocated to one user, the faster the communication speed.
[0024]
Next, an uplink / downlink data collision prevention method in bidirectional communication will be described. Generally, a distribution line has a large number of branches, and collision of upstream and downstream data is expected due to reflection at a branch point. Therefore, it is desirable to distinguish upstream and downstream data by frequency or time. Hereinafter, a method for frequency dividing uplink / downlink data will be described.
FIG. 6A shows the IFFT circuit diagram of the master station, and FIG. 6B shows the IFFT circuit diagram of the slave station. In FIG. 6 (a), downlink data is assigned to a high frequency part on the frequency axis, and in FIG. 6 (b), uplink data is assigned to a low frequency part on the frequency axis. In this way, frequency division is performed in uplink and downlink to perform full-duplex communication (Frequency Division Duplex; FDD). Thereby, the collision of the uplink / downlink data can be prevented.
[0025]
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 the downlink data, and a narrow band is allocated to the uplink data.
In the implementation 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, the uplink and downlink variable frequency bands that can be assigned to both are assigned. It may be provided. FIG. 7 is a diagram in which these three types of frequency bands are drawn in one IFFT circuit diagram.
[0026]
Further, it is possible to abolish fixed frequency bands for uplink and downlink and make them all variable frequency bands.
The procedure for assigning the variable frequency band to the master station or slave station will be described.
(1) At the time of entry request, the slave station adds information on the communication type (web (WWW), video conference, etc.) and sends it to the master station.
(2) The master station determines the allocation of uplink and downlink frequency bands according to the communication type. Specifically, in the case of WWW, the amount of downlink data is much larger than the amount of uplink data, so more downlink frequency bands are allocated than the uplink frequency band. In the case of a video conference, the uplink and downlink data amounts are almost the same, so the downlink frequency band and the uplink frequency band are allocated to the same extent. The master station uses slot 1 to transmit the frequency allocation information to all the slave stations.
[0027]
(3) The slave station changes the allocation of the input signal to the IFFT circuit based on this allocation information.
As a method of performing frequency division full-duplex communication, there is a method of changing the frequency of a carrier wave used in uplink and downlink, in addition to a method of assigning an input signal to the IFFT circuit of the OFDM modulation unit.
Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-described embodiments. In the above embodiment, the uplink and downlink separate frequency bands are assigned to the time slots to prevent interference in the distribution lines. However, as shown in FIG. May be performed. Further, as shown in FIG. 9, a time slot can be used for every one hour segment in an ascending / descending manner.
[0028]
【The invention's effect】
According to the onset light as described above, reduces the waste of not used slots as much as possible, it is possible to realize a system of communication efficiency.
[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;
6A is a IFFT circuit diagram of a master station, and FIG. 6B 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 when full-duplex communication is performed by time division in uplink and downlink.
FIG. 9 is a time slot diagram when a time slot is used for every one hour segment in uplink and downlink alternation.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Slot allocation control part 2 Modem 3 Error correction encoding circuit 4 Interleaving circuit 5 Serial / parallel conversion circuit 6 PSK or QAM encoding circuit 7 IFFT (inverse Fourier transform) circuit 8 Parallel / serial conversion circuit 9 Guard interval insertion circuit 10 D / A conversion circuit 11 Orthogonal modulation circuit 12 Mixer 21 Mixer 22 Orthogonal 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

Claims (9)

In a multiplex communication system in which data communicated between a master station and a slave station connected by a power line network is placed in a time slot divided by the TDMA system and bidirectional communication is performed between the master and slave stations.
In the master station, provided with an allocation control means for changing the setting of the time slot allocation information according to the number of slave stations existing in the network ,
If the assignment information is not changed by the assignment control means even if the slave station makes an entry request, the waiting time until the slave station makes an entry re-request to the master station is set differently for each slave station. A multiplex communication system in power line carrier. 2. The multiplex communication in power line carrier according to claim 1, wherein said allocation control means sets the number of time slot allocations in said time slot allocation information equal to the number of slave stations connected to said power line network. system.   2. The multiplex communication system for power line carrier 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 assigned to communication data from a master station to a slave station, and a relatively narrow frequency band is assigned to communication data from the slave station to the master station. Communication system in power line carrier.   4. The power line carrier multiplexing according to claim 3, wherein a frequency band assigned to communication data from the master station to the slave station or a frequency band assigned to communication data from the slave station to the master station is made variable. Communications system.   2. The multiplex communication system in power line carrier 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. Communication system in power line carrier.   7. The power line carrier multiplexing according to claim 6, wherein a time band assigned to communication data from the parent station to the child station or a time band assigned to communication data from the child station to the parent station is made variable. Communications system. A multiplex communication method in which data communicated between a master station and a slave station connected by a power line network is placed in a time slot divided by the TDMA method, and bidirectional communication is performed between the master and the slave stations,
A multiplex communication method in power line carrier, including the following procedure for changing the setting of the number of timeslot allocations according to the number of slave stations existing in the network.
(1) The master station outputs the time slot delimiter and allocation information to all the slave stations in the first slot.
(2) The slave station requesting entry places entry request information for the master station in the second slot.
(3) The master station determines the allocation number based on the entry request content of the second slot, and outputs the slot information allocated to the new user in the first slot of the next time segment.
  (4) If the entry request from the slave station does not reach the master station for some reason, Since no allocation information is recorded in the first slot from the master station, the slave station determines that the entry request has not reached the master station according to the contents of the first slot of the next time segment, and sets each slave station The entry request is made again based on the different waiting times.
(5) When the slave station receives the allocation information of the first slot, the slave station outputs it with confirmation.
(6) When the master station receives confirmation from the slave station, the master station determines the allocation information for the first slot.

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