JP2003244038A - Modem for power line communication - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a MODEM for power line communication capable of taking the best impedance matching with a distribution line at all times so as to maintain the communication quality. <P>SOLUTION: The MODEM includes: a variable impedance circuit 12 capable of varying input output impedance; a band pass filter 16 for transmitting a transmission test signal to extract a component of the transmission signal included in a received signal; and a control circuit 17 for detecting a level of a signal extracted from the band pass filter 16 and controlling the variable impedance circuit 12 to minimize a crosstalk level. Thus, the input output impedance is best set in matching with the impedance of the distribution line. Even when the impedance of the distribution line is temporally changed, the input output impedance of the MODEM is made to follow up the change. <P>COPYRIGHT: (C)2003,JPO

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 communication system for performing communication using a power line network via a distribution line.

[0002]

2. Description of the Related Art Power line carrier uses a power distribution line to
This is a technique for transmitting data to users such as ordinary homes and offices (see Japanese Patent Laid-Open No. 10-145265). Figure 3
It is an overall schematic diagram of a power line carrier communication system. A single-phase three-wire type low-voltage distribution line (hereinafter simply referred to as “distribution line”) 2 is connected from a high-voltage distribution line 1 through a pole transformer 3, and a plurality of consumers 8 are connected to the ends thereof.

The distribution line 1 on the primary side of the pole transformer 3
Is usually a three-phase type, and the distribution line 2 on the secondary side of the pole transformer 53 is a single-phase three-wire type. A power line network composed of distribution lines 2 in units of such pole transformers is called a "transformer section network" (in contrast,
Internet, etc. will be higher-level networks). An optical / electrical converter (O /
E) 5, a PLT modem (referred to as a parent modem) 6 is connected, and the parent modem 6 is connected to the trans section network.

In homes and offices that serve as terminals of each transformer section network, information terminal devices such as personal computers and televisions are connected through a PLT modem (referred to as a terminal modem) 9.

[0005]

The input / output impedance of the terminal modem is preferably matched with the characteristic impedance of the distribution line. However, the power line communication system
Because the track is not designed for data communication,
The characteristic impedance of distribution lines often does not have a constant value. In addition, the impedance changes even if electrical equipment is connected at home or the switch is turned on or off. The range of the change ranges from several Ω to several hundred Ω.

When a terminal modem is connected to such a distribution line and the input / output impedance thereof is fixed to a constant value, the impedance of the distribution line changes with time due to changes in the electrical equipment configuration in the home as described above. Change in impedance, impedance mismatch occurs and signal reflection occurs. Therefore, it is an object of the present invention to realize a power line carrier communication modem capable of always obtaining the best impedance matching with a distribution line and maintaining communication quality.

[0007]

Means for Solving the Problems and Effects of the Invention A power line carrier communication modem according to the present invention includes a transmitter, a receiver, an impedance adjusting circuit capable of changing input and output impedances, and a receiver for receiving. An extraction circuit for extracting a component of a transmission signal to be transmitted from the transmitter, which is included in the received signal to be detected, and an extraction signal level of the extraction circuit is detected to control the impedance adjustment circuit so as to minimize a crosstalk level. And a control means for performing the operation (claim 1).

The input / output impedance of the modem can be adjusted so that the level of the transmission signal transmitted from the transmitter and sneaking into the receiver is minimized. As a result, the input / output impedance of the modem can be set to the best value according to the impedance of the distribution line. Even if the impedance of the distribution line changes with time, the input / output impedance of the modem can be made to follow it, so that impedance matching can always be obtained and communication quality can be maintained.

When performing frequency division duplex communication in which the frequency bands of the upstream and downstream signals are divided, the extraction circuit may be a bandpass filter that passes the frequency components of the transmission signal transmitted from the transmitter. (Claim 2).

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a diagram of a power line carrier communication system in a customer. The distribution line 2 on the secondary side of the pole transformer is drawn into the house. The terminal modem 9 is connected to an electric outlet in the house. To describe the connection mode between the terminal modem 9 and the distribution line 2 in detail, if the single-phase three-wire type voltage line H and neutral line C are used for the communication line, the terminal modem 9 uses the voltage line H and neutral line. Connected to line C. If both voltage lines H, H of the single-phase three-wire type are used, the terminal modem 9 is connected to the both voltage lines H, H. FIG. 1 shows an example in which the voltage line H and the neutral line C are used for the communication line.

In this power line carrier communication system, communication between the master station and each terminal modem 2 is performed by frequency division duplex (FDD) in which the frequency bands of the upstream and downstream signals are divided.
sionDuplex) is used for full duplex. Figure 2
FIG. 3 is a block diagram showing an internal configuration of the terminal modem 9.
The line connected to the electrical outlet is connected to the variable impedance circuit 12 through the capacitor C0.
The variable impedance circuit 12 is composed of a variable resistor connected in parallel to the line. By changing the resistance value of this variable resistor from a control circuit (described later), the terminal modem 9
The input / output impedance of can be changed.

Incidentally, instead of the variable resistor, a plurality of fixed resistors may be connected and switched by a switch to change the input / output impedance stepwise. The terminal modem 9 includes a hybrid circuit 13, a transmission amplifier 14,
A reception amplifier 15 and a modem main body 18 that processes a transmission / reception signal are provided. Further, a bandpass filter 16 having a pass frequency band of a transmission signal is connected to the output end (or the input end) of the reception amplifier 15, and the signal passed through the bandpass filter 16 is input to the control circuit 17. There is.

The control circuit 17 is a microcomputer,
It has a configuration including an input / output interface and a memory. The control signal output from the control circuit 17 is supplied to the variable impedance circuit 12. The function of the control circuit 17 is that the signal is sent from the modem main body 18 at a known level when the signal from the parent modem 6 is not received, and the transmission amplifier 14
Of the transmission signal amplified in step 1, the hybrid circuit 13 is circulated to enter the reception amplifier 15, the level of the frequency component extracted by the bandpass filter 16 is detected, and the variable impedance is adjusted to minimize the level. Circuit 1
2 is to adjust the impedance.

When the impedance of the distribution line and the impedance of the hybrid circuit 13 are matched, the transmission signal is transmitted to the distribution line, and the proportion of the transmission signal circling to the receiving side is reduced. When the impedance of the distribution line and the impedance of the hybrid circuit 13 are not matched, the ratio of the power sneaking into the receiving side increases, and it becomes a noise source to the receiving side. Therefore, a signal is sent from the modem main body 18 at a known level, the control circuit 17 detects the signal level sneaking into the receiving side, and the impedance of the variable impedance circuit 12 is adjusted so that this level is minimized. Impedance matching between the electric wire and the terminal modem 9 can be achieved.

The signal sent from the modem main body 18 is a signal used by the terminal modem 9 for self-adjustment, and the parent modem 6 receiving this signal can recognize that it is a test of the terminal modem 9. It is advisable to superimpose a code having a special meaning. Since the impedance of the distribution line changes when connecting or disconnecting other electric devices, the control circuit 17
It is preferable to perform the adjusting operation of 1 to a plurality of times in a day. For example, it may be performed at a fixed time of the day, or may be performed every tens of minutes to several hours.

Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-mentioned embodiments, and various modifications can be made within the scope of the present invention. .

[Brief description of drawings]

FIG. 1 is a diagram of a power line carrier communication system in a customer.

FIG. 2 is a block diagram showing an internal configuration of a terminal modem 9.

FIG. 3 is an overall schematic diagram of a power line carrier communication system.

[Explanation of symbols]

1 High voltage distribution line 2 distribution lines (secondary side) 3 pole transformer 4 optical fiber 5 O / E converter 6 parent modem 8 consumers 9 terminal modem 12 Variable impedance circuit 13 Hybrid circuit 14 Transmitter amplifier 15 Receiver amplifier 16 bandpass filter 17 Control circuit 18 modem body

Claims (2)

[Claims] 1. A power line carrier communication modem used in a power line carrier communication system for performing communication using a power line network via a distribution line, comprising: an impedance adjusting circuit capable of changing input / output impedance; An extraction circuit for extracting the component of the transmission signal included in the signal, and a control means for detecting the extraction signal level of the extraction circuit and controlling the impedance adjustment circuit so that the crosstalk level is minimized. A power line carrier communication modem. 2. The modem for power line carrier communication according to claim 1, wherein the frequency division duplex communication is performed by dividing the frequency band of the upstream and downstream signals, wherein the extraction circuit passes the frequency component of the transmission signal. A power line carrier communication modem characterized by being a bandpass filter.