JPWO2007026413A1 - Power line carrier communication modem - Google Patents

Abstract

A power line carrier communication modem capable of dynamically following the changing transmission path characteristics even when the signal attenuation characteristics on the transmission path greatly differ depending on the frequency band. A power line carrier communication modem 100 including a coupler 10, a receiver circuit 20, a driver circuit 40, and a modulation / demodulation circuit 30, and using a power line 1 as a transmission line, a preamplifier 52 having a variable signal gain and a filter having a variable frequency characteristic The circuit further includes an equalizer circuit 50 formed by connecting the circuit 51 in series, and the modulation / demodulation circuit 30 monitors a known signal within the communication band included in the received signal received from the power line 1, and receives the gain of the received signal and the frequency of the received signal. Transmission path estimation means 32 for estimating the characteristics as transmission path characteristics, and equalizer control means 33 for changing the signal gain of the preamplifier 52 and the frequency characteristics of the filter circuit 51 so as to compensate the transmission path characteristics estimated by the transmission path estimation means. With.

Description

  The present invention relates to a power line carrier communication modem for improving communication performance in a power line carrier communication system using an existing power line as a transmission line.

  In power line communication (Power Line Communication: hereinafter referred to as “PLC”) in which communication is performed using an existing power line as a transmission line, it is impossible to uniquely determine the characteristics of the transmission path. In other words, the transmission path characteristics change according to the installation state of the power line or the operation status of the connected device. In order to realize the PLC in such a situation, it is necessary to have a function of constantly monitoring the transmission path characteristics and performing communication adapted to the transmission path characteristics that vary depending on location and time.

  As a communication method adapted to such a changing transmission line characteristic, a method realized by a function of a digital modulation / demodulation method is generally studied. On the other hand, a circuit system adapted to such transmission line characteristics with an analog circuit is also possible. As an example, there is a power line communication modem in which an equalizer circuit is provided in the receiving circuit to improve the accuracy of correlation peak detection for demodulation. (For example, refer to Patent Document 1). In general, a method for performing frequency compensation by an equalizer circuit in communication with high attenuation in a high frequency band is a known technique.

Japanese Patent Laid-Open No. 3-44125 (first page, FIG. 1)

  However, the prior art has the following problems. Patent Document 1 does not describe a method for controlling an equalizer circuit. In order to improve communication performance when there is a change in transmission path (power line) characteristics depending on time and place, a circuit system that can dynamically follow the changing transmission path characteristics is required.

  A communication method adapted to the transmission path characteristics is a general technique in digital modulation / demodulation. However, when waveform compensation adapted to the transmission path characteristics is not performed in the analog circuit, there are the following problems. That is, when the signal attenuation characteristics on the transmission line are greatly different depending on the frequency band, there is a problem that the amplitude of the input signal over a wide band cannot be efficiently input to the input range of the AD converter.

  The present invention has been made to solve the above-described problems, and can dynamically follow the changing transmission line characteristics even when the signal attenuation characteristics in the transmission line vary greatly depending on the frequency band. An object is to obtain a power line carrier communication modem.

  A power line carrier communication modem according to the present invention includes a coupler, a receiver circuit, a driver circuit, and a modulation / demodulation circuit. In a power line carrier communication modem using a power line as a transmission line, a receiver circuit and a modem circuit that constitute a reception circuit In addition, an equalizer circuit formed by connecting in series a preamplifier having a variable signal gain and a filter circuit having a variable frequency characteristic is provided. The modulation / demodulation circuit is connected to the power line via a coupler, a receiver circuit, and an equalizer circuit. Transmission path estimation means for monitoring a known signal within a communication band included in the received reception signal and estimating the gain of the reception signal and the frequency characteristics of the reception signal as transmission path characteristics, and the transmission path estimated by the transmission path estimation means Equalizer control method that changes the signal gain of the preamplifier and the frequency characteristics of the filter circuit to compensate for the characteristics It is those with a door.

  In addition, a power line carrier communication modem according to the present invention includes a coupler, a receiver circuit, a driver circuit, and a modem circuit, and in the power line carrier communication modem using a power line as a transmission line, a modem circuit and a driver circuit constituting a transmission circuit And a pre-emphasis circuit in which a preamplifier having a variable signal gain and a filter circuit having a variable frequency characteristic are connected in series, and the modulation / demodulation circuit is received from the power line via the coupler and the receiver circuit. A transmission path estimating means for monitoring a known signal in a communication band included in the received signal and estimating the gain of the received signal and the frequency characteristic of the received signal as the transmission path characteristics; and a transmission path in the power line carrier communication modem on the receiving side The preamplifier signal gain and the gain are received so as to receive the transmission path characteristics estimated by the estimation means and compensate the transmission path characteristics. It is obtained by a pre-emphasis control means for changing the frequency characteristic of the filter circuit.

  According to the present invention, a circuit (equalizer circuit or pre-emphasis circuit) that compensates transmission path characteristics is mounted on a reception circuit or transmission circuit configured by an analog circuit, and the transmission path characteristics are periodically monitored and transmitted. If the characteristics of the path change, the appropriate circuit parameters are dynamically controlled, so that even if the signal attenuation characteristics vary greatly depending on the frequency band, the transmission path varies. A power line carrier communication modem that can dynamically follow the characteristics can be obtained.

It is a circuit block diagram of the power line carrier communication modem in Embodiment 1 of this invention. It is explanatory drawing which produces | generates a compensation signal from the received signal in Embodiment 1 of this invention. It is a flowchart regarding the production | generation of the compensation signal in Embodiment 1 of this invention. It is a circuit block diagram of the power line carrier communication modem in Embodiment 2 of this invention. It is a circuit block diagram of the power line carrier communication modem in Embodiment 3 of this invention. It is explanatory drawing regarding compensation of the transmission signal by the pre-emphasis circuit 70 in Embodiment 3 of this invention.

  Hereinafter, preferred embodiments of a power line carrier communication modem of the present invention will be described with reference to the drawings. The power line carrier communication modem of the present invention is equipped with a compensation circuit (equalizer circuit or pre-emphasis circuit) for transmission path characteristics, and based on monitoring of a known signal in a communication band included in a received signal, the signal gain of the compensation circuit and By changing the frequency characteristic, it is possible to dynamically follow the changing transmission line characteristic.

Embodiment 1 FIG.
FIG. 1 is a circuit configuration diagram of a power line carrier communication modem according to Embodiment 1 of the present invention. 1 includes a coupler 10, an LNA (Low Noise Amplifier) 20 that is a receiver circuit, a modulation / demodulation circuit 30, a power amplifier 40 that is a driver circuit, and an equalizer circuit 50 provided on the receiving circuit side. Composed.

  The power line carrier communication modem 100 is connected to the power line 1 which is a transmission path via a coupler 10. Furthermore, an equalizer circuit 50 is provided between the LNA 20 and the modem circuit 30 in the analog reception circuit of the first embodiment. The equalizer circuit 50 is configured by connecting a filter circuit 51 and a preamplifier 52 in series.

  In the filter circuit 51, some of the elements that determine the filter characteristics are configured by variable elements. Specifically, as shown in FIG. 1, the filter circuit 51 includes a variable resistor that can change a resistance value that determines a filter characteristic. The preamplifier 52 has a configuration that can vary the gain of the output signal. Specifically, as shown in FIG. 1, the preamplifier 52 includes a variable resistor that can change a resistance value that determines an output signal level.

  Further, the modem circuit 30 includes an AD converter 31, a transmission path estimation unit 32, and an equalizer control unit 33.

  The transmission path estimation means 32 estimates the transmission path characteristics of the power line 1 using a known signal (pilot signal) included in the received signal. Specifically, the transmission path estimation means 32 converts the known signal in the communication band included in the received signal received from the power line 1 via the coupler 10, LNA 20 and equalizer circuit 50 and further via the AD converter 31. Based on this, the transmission line characteristics of the power line 1 are estimated.

  Further, the equalizer control means 33 changes the variable resistance value of the filter circuit 51 and further changes the variable resistance value of the preamplifier 52 based on the transmission path characteristics estimated by the transmission path estimation means 32. As a result, the equalizer circuit 50 can output a compensation signal capable of obtaining communication performance adapted to the current transmission path characteristics, and can dynamically follow the changing transmission path characteristics.

FIG. 2 is an explanatory diagram for generating the compensation signal S _C from the reception signal S _{R according} to Embodiment 1 of the present invention. Received signal S _R shown in Figure 2, low, mid as a specific band, the three bands of the wide area, respectively illustrates the case containing the pilot signals P1 to P3.

  The power line carrier communication modem 100 that performs communication using the power line 1 according to the present invention outputs an OFDM (Orthogonal Frequency Division Multiplexing) modulated wave of a wide band (for example, 5 MHz to 35 MHz). Here, as shown in FIG. 2, the power line carrier communication modem 100 on the transmission side converts the low band pilot signal P1, the mid band pilot signal P2, and the high band pilot signal P3 into sub-modulated waves. Allocate to carriers (total 3) and transmit.

  On the other hand, the transmission path estimation means 32 of the power line carrier communication modem 100 on the receiving side monitors the signal levels of the pilot signals P1 to P3 included in the received signal and estimates the attenuation characteristics of the transmission path. For example, when it is determined from the reception state of each pilot signal P1 to P3 that the attenuation at a high frequency is larger, the value of the variable resistance of the filter circuit 51 is increased to increase the HPF (High Pass Filter) type. The filter attenuation slope is increased and the amplification gain of the preamplifier is appropriately controlled.

As a result, the equalizer circuit functions so as to compensate the frequency characteristic in the transmission line, and the signal input to the modulation / demodulation circuit is obtained in a state where the frequency characteristic is flat as in the compensation signal S _C shown in FIG. Can do. As a result, a received signal in a wider band is efficiently input to the input range of the AD converter 31 and the reception performance is improved.

The generation of the compensation signal S _C by the transmission path estimation unit 32 and the equalizer control unit 33 will be described more specifically. FIG. 3 is a flowchart relating to the generation of the compensation signal S _{C in} the first embodiment of the present invention. Here, as shown in FIG. 2, the generation of the compensation signal S _C based on the received signal S _R including the three pilot signals P1 to P3 will be described.

First, in step S301, channel estimation means 32 observes the receiving level of the pilot signal P1~P3 included in the received signal S _R. The pilot signals P1 to P3 are known signals, and the transmission path estimation means 32 has a signal level as a specified value in advance when the pilot signals P1 to P3 are received without attenuation.

  Next, in step S302, the transmission path estimation unit 32 determines the current transmission path characteristics based on the difference between the reception levels of the pilot signals P1 to P3 observed in the previous step S301 and the predetermined value that is held in advance. Is estimated. Specifically, the transmission path estimation means 32 determines a variable resistance value that is a setting parameter of the filter circuit 51 so that the signal strengths of the pilot signals P1 to P3 are equal.

  Next, in step S303, the equalizer control unit 33 changes the variable resistance value of the filter circuit 51 according to the variable resistance value determined by the transmission path estimation unit 32 in the previous step S302. As a result, the signal strength approaches a certain level over the frequency band, but the signal strength is different from a desired specified value.

  Next, in step S304, the transmission path estimation means 32 sets the difference between the signal level of the pilot signals P1 to P3 after changing the variable resistance value of the filter in the previous step S303 and a predetermined value that is held in advance. Based on this, the current transmission path characteristics are estimated. Specifically, the transmission path estimation means 32 determines the variable resistance value that is the setting parameter of the preamplifier 52 so that the signal strengths of the pilot signals P1 to P3 approach the specified values.

The equalizer control means 33 changes the variable resistance value of the preamplifier 52 according to the variable resistance value determined by the transmission path estimation means 32. Thereby, finally, the setting parameter of the equalizer circuit can be dynamically adjusted to the current transmission path characteristics, and the received signal can be obtained as the compensation signal S _{C in} a desired state approaching the known signal strength. . As a result, a wide band compensated received signal is efficiently input to the input range of the AD converter 31 and reception performance is improved.

  According to the first embodiment, it is possible to compensate the characteristics of the transmission line (power line) by the analog circuit by mounting the equalizer circuit in the receiving circuit unit of the power line carrier communication modem. Also, the transmission line (power line) characteristics are periodically monitored using known signals (pilot signals), and the equalizer circuit parameters are determined so as to compensate for the estimated characteristics. However, the communication performance can be dynamically set to the best state.

  In the above description, the number of pilot signals is three. However, the power line carrier communication modem of the present invention is not limited to this. More pilot signals may be used to improve the accuracy of transmission path estimation. However, if the number of pilot signals is increased, the number of subcarriers that can be used for the original communication is reduced, so it is necessary to consider that the communication speed deteriorates.

  In the flowchart of FIG. 3, the two-stage method of changing the variable resistance value of the preamplifier 52 after changing the variable resistance value of the filter circuit 51 has been described. However, the parameters of the power line carrier communication modem of the present invention are described. The changing method is not limited to this. It is also possible to simultaneously change the variable resistance values of both the filter circuit 51 and the preamplifier 52 on the basis of the difference between the reception levels of the pilot signals P1 to P3 and the predetermined value that is previously held.

Embodiment 2. FIG.
In the first embodiment, a case has been described in which a pilot signal for observing the transmission path characteristics is embedded in a part of the received signal, so that the parameters of the equalizer circuit are dynamically changed according to the transmission path characteristics. . In the second embodiment, the parameters of the equalizer circuit are dynamically changed in accordance with the transmission path characteristics by embedding the transmission path estimation packet specified for observing the transmission path in a plurality of packets to be communicated. The case where it does is demonstrated.

  FIG. 4 is a circuit configuration diagram of the power line carrier communication modem according to the second embodiment of the present invention. Compared with the circuit configuration diagram of the power line carrier communication modem of FIG. 1 in the first embodiment, FIG. 4 is different in that it further includes a bypass switch 60 for bypassing the equalizer circuit. It is the same composition.

  In the second embodiment, the transmission path estimation means 32 estimates the transmission path characteristics of the power line using the transmission path estimation packet (training packet) by the following method. Here, the transmission path estimation packet is a special packet defined for estimating transmission path characteristics.

  FIG. 2 used in the description of the first embodiment shows one packet in which three pilot signals P1 to P3 are embedded, but the transmission path estimation packet in the second embodiment is several tens to several. This corresponds to a packet filled with one hundred pilot signals. That is, the transmission path estimation packet is a special packet composed of known signals over the entire communication band.

  Since such a transmission path estimation packet is embedded between packets used for normal communication, it is periodically issued mainly when the communication load is relatively small. The transmission path estimation packet issued on the transmission side is monitored on the reception side, and the transmission path characteristics are estimated by comparing the known signal level with the received signal level.

  The timing for issuing the transmission path packet is assumed to be when the communication load is low so as not to affect the communication performance. All of the transmission path estimation packets are composed of known signals and do not include signals used for original communication. Therefore, when performing transmission path estimation, the equalizer control means 33 controls the bypass switch 60 so as to bypass the equalizer circuit 50. Thereby, the transmission path estimation means 32 can receive a transmission path estimation packet as a received signal reflecting the characteristics of the power line 1 and can perform transmission path estimation.

  The equalizer control means 33 changes the elements of the equalizer circuit 50 so as to compensate for the characteristics of the transmission line, and then performs switch control of the bypass switch 60 to set the normal communication mode state.

  According to the second embodiment, the equalizer circuit is mounted on the receiving circuit unit of the power line carrier communication modem, so that the transmission path (power line) characteristic compensation by the analog circuit is performed using the transmission path estimation packet (training packet). It can be carried out. Since the transmission path estimation packet is periodically issued when the communication load is low, the communication speed is not deteriorated. Furthermore, unlike a method using a pilot signal in a communication band, subcarriers are not wasted and communication speed deterioration can be prevented.

Embodiment 3 FIG.
In the first and second embodiments, the case has been described in which the equalizer circuit 50 is inserted on the receiving circuit side in order to improve the communication performance in accordance with the dynamically changing transmission line characteristics. In the third embodiment, a power line carrier communication modem 100 that improves communication performance on the transmission circuit side will be described.

  FIG. 5 is a circuit configuration diagram of a power line carrier communication modem according to Embodiment 3 of the present invention. The power line carrier communication modem 100 shown in FIG. 5 includes a coupler 10, an LNA (Low Noise Amplifier) 20 as a receiver circuit, a modulation / demodulation circuit 30, a power amplifier 40 as a driver circuit, and a pre-emphasis circuit 70 provided on the transmission circuit side. Consists of.

  The power line carrier communication modem 100 is connected to the power line 1 which is a communication path via a coupler 10. A pre-emphasis circuit 70 is provided in the analog transmission circuit. The pre-emphasis circuit 70 is configured by connecting a filter circuit 71 and a preamplifier 72 in series.

  In the filter circuit 71, a part of the elements that determine the filter characteristics are composed of variable elements. Specifically, as shown in FIG. 5, the filter circuit 71 includes a variable resistor that can change a resistance value that determines a filter characteristic. The preamplifier 72 has a configuration that can vary the gain of the output signal. Specifically, as shown in FIG. 5, the preamplifier 72 includes a variable resistor that can change a resistance value that determines an output signal level.

  Further, the modem circuit 30 includes an AD converter 31, a transmission path estimation unit 32, and a pre-emphasis control unit 34.

  In the first or second embodiment, the power line carrier communication modem 100 that has received the signal compensates the received signal. In contrast, in the third embodiment, the power line carrier communication modem 100A that has received the signal is notified of the transmission path estimation result to the power line carrier communication modem 100B that is the signal transmission source, whereby the power line carrier communication modem The parameters of the pre-emphasis circuit 70 in 100B are changed to compensate the transmission signal itself.

  The specific transmission path estimation method is as follows. First, the power line carrier communication modem 100A on the receiving side issues a transmission request for a pilot signal or a transmission path estimation packet as a known signal to the power line carrier communication modem 100B of the transmission source. In response to this, the power line carrier communication modem 100B receiving the transmission request transmits a known signal to the power line carrier communication modem 100A.

  Thereafter, when the power line carrier communication modem 100A receives a known signal from the power line carrier communication modem 100B via the AD converter 31, the transmission line estimation means 32 performs transmission path estimation to determine circuit parameters. For the transmission path estimation and circuit parameter determination by the transmission path estimation means 32, the method described in the first embodiment or the second embodiment can be applied.

  Then, the power line carrier communication modem 100A notifies the power line carrier communication modem 100B of the circuit parameter result determined by the transmission path estimation means 32, and issues a request to change the parameters of the pre-emphasis circuit 70 of the power line carrier communication modem 100B. . In response to this, the pre-emphasis control means 34 of the power line carrier communication modem 100B changes the parameters of the pre-emphasis circuit 70.

  From the above result, for example, when it is determined that the attenuation at high frequency is larger, the value of the variable resistance of the filter circuit 51 is increased to increase the HPF (High Pass Filter) type filter attenuation slope. At the same time, the amplification gain of the preamplifier is appropriately controlled.

FIG. 6 is an explanatory diagram relating to transmission signal compensation by the pre-emphasis circuit 70 according to the third embodiment of the present invention. When it is determined that the power line carrier communication modem 100A on the reception side has a higher attenuation at high frequencies, the signal strength from the power line carrier communication modem 100B on the transmission side becomes high at high frequencies as shown in FIG. transmitting a pre-emphasis output S _P. At this time, the transmission signal needs to be set to be equal to or less than the specified value of the leakage electromagnetic field.

As a result, the pre-emphasis circuit 70 of the power line carrier communication modem 100B on the transmission side functions so as to compensate for the frequency characteristics of the transmission path. On the other hand, the power line carrier communication modem 100A of the receiving side through a transmission path, the frequency characteristics of the input signal can be received as a flat state (see the waveform of the received spectrum S _R and DA converter output S _DA in FIG. 6). As a result, a received signal in a wider band is efficiently input to the input range of the AD converter 31 of the power line carrier communication modem 100A on the receiving side, and communication performance is improved.

  According to the third embodiment, the pre-emphasis circuit is mounted on the transmission circuit unit of the power line carrier communication modem, so that the characteristics of the transmission line (power line) by the analog circuit can be compensated. In addition, the transmission line characteristic of the power line carrier communication modem on the reception side is monitored using a known signal (pilot signal or transmission line estimation packet), and the power line carrier communication modem on the transmission side is compensated for the estimated characteristic. Since the parameters of the pre-emphasis circuit are determined, the communication performance can be dynamically optimized even when the power line characteristics fluctuate.

In the above description, the case where the equalizer circuit is provided on the receiving circuit side is described in Embodiments 1 and 2, and the case where the pre-emphasis circuit is provided on the transmission circuit side is described in Embodiment 3. However, a configuration having both an equalizer circuit and a pre-emphasis circuit is also possible. By coexisting both circuits, it can be expected to further improve the transmission path application accuracy.

Claims (4)

In a power line carrier communication modem comprising a coupler, a receiver circuit, a driver circuit, and a modem circuit, and using a power line as a transmission line,
Further comprising an equalizer circuit formed by serially connecting a preamplifier having a variable signal gain and a filter circuit having a variable frequency characteristic between the receiver circuit and the modulation / demodulation circuit constituting the reception circuit,
The modem circuit is:
A known signal in a communication band included in a received signal received from the power line via the coupler, the receiver circuit, and the equalizer circuit is monitored, and a gain of the received signal and a frequency characteristic of the received signal are transmitted on a transmission line Transmission path estimation means for estimating the characteristics;
Equalizer control means for changing the signal gain of the preamplifier and the frequency characteristics of the filter circuit so as to compensate for the transmission path characteristics estimated by the transmission path estimation means, . In a power line carrier communication modem comprising a coupler, a receiver circuit, a driver circuit, and a modem circuit, and using a power line as a transmission line,
A pre-emphasis circuit formed by serially connecting a preamplifier having a variable signal gain and a filter circuit having a variable frequency characteristic between the modulation / demodulation circuit and the driver circuit constituting the transmission circuit;
The modem circuit is:
Transmission for monitoring a known signal in a communication band included in a received signal received from the power line via the coupler and the receiver circuit, and estimating a gain characteristic of the received signal and a frequency characteristic of the received signal as a transmission line characteristic A route estimation means;
The pre-amplifier changes the signal gain of the preamplifier and the frequency characteristic of the filter circuit so as to receive the transmission line characteristic estimated by the transmission line estimation means in the power line carrier communication modem on the receiving side and compensate the transmission line characteristic. A power line carrier communication modem comprising: an emphasis control means. The power line carrier communication modem according to claim 1 or 2,
The power line carrier communication modem characterized in that the transmission path estimation means monitors a pilot signal of a specific band included in the received signal as the known signal and estimates the transmission path characteristics. The power line carrier communication modem according to claim 1 or 2,
The power line carrier communication modem characterized in that the transmission path estimation means monitors a transmission path estimation packet included in a packet received as the received signal as the known signal and estimates the transmission path characteristics.

Images