JP2002319919A - Power line communication apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power line communication apparatus, with which a communication quality or waste of transmitting power can be improved on the basis of SNR estimation related to a power line. SOLUTION: In the power line communication apparatus provided with a symbol mapper for generating a prescribed modulated signal from a plurality of modulation systems by distributing transmitting data to a plurality of quadrature carrier waves partially overlapping respective frequency components as a transmitting system at least, an inverse Fourier transforming means for outputting an OFDM signal by multiplexing the modulated signal in a time area, a Fourier transforming means for generating a plurality of quadrature carrier waves from the received OFDM signal as a receiving system and a symbol demapper for performing prescribed demodulating processing, a large number of received signals are sampled in the output of the Fourier transformation means for each carrier wave, an SNR is estimated by finding a noise power (N) from an average signal(S) and the distribution characteristics of noise components and required communication control is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power line communication device, and more particularly, to a signal to noise ratio (S) related to a power line as a transmission line.
The present invention relates to means for estimating an ignal to noise ratio (hereinafter, referred to as SNR) to improve communication quality.

[Prior art]

[0002]

2. Description of the Related Art In power line communication, information is transmitted using a power line provided to supply electric power such as an outdoor power distribution line or an indoor power line, and it is necessary to newly lay a communication line. Communication costs can be reduced
Conventionally, various methods have been studied. In power line communication, while having the above advantages, a power line having poor transmission characteristics due to noise or the like is used. Therefore, it is necessary to use a communication method that is resistant to noise.

[0003] Orthogonal Frequenc
y Division Multiplexing (hereinafter referred to as OFDM)
A type of multi-carrier modulation system in which channel data is distributed over multiple carriers and transmitted.Data is distributed over multiple carriers, which reduces the probability of all data being lost due to noise. Known as the scheme.

FIG. 4 is a functional block diagram showing a configuration example of a conventional power line communication device using the OFDM system. The power line communication device shown in FIG.
A / A converter (digital / analog converter) 110 and an intermediate frequency / high frequency processing unit (hereinafter, IF / RF)
Along with connecting to 130, the IF / RF processing unit 130 as a receiving system is an anti-aliasing filter (low-pass filter) 140 and an A / D converter (analog / digital converter).
It is configured by connecting to the OFDM demodulation unit 200 via 150.

[0005] The OFDM system is described in detail in, for example, "Makoto Itami, OFDM Modulation Technology, Trikeps, March 2000", and so only the main points will be described here. OF
The DM modulating unit 100 generates a predetermined modulated signal by dispersing transmission data to a plurality of orthogonal carrier waves with each frequency component partially overlapping, and an S / S converter for converting serial data to parallel data. A P conversion circuit 102 and an inverse fast Fourier transformer (Inverse Fas
t Fourier Transform, hereinafter referred to as IFFT) 103, and a P / S conversion circuit 104 for converting parallel data into serial data.
And a transmission-side guard interval circuit 105 for reducing the influence of multipath due to a reflected wave from a transmission line (power line) branch.

[0006] The OFDM demodulation unit 200 receives a guard interval circuit 201 on the receiving side, an S / P conversion circuit 202,
A fast Fourier transformer (Fast Transformer) as a Fourier transform means for generating the plurality of orthogonal carriers from an FDM signal.
Fourier Transform (hereinafter referred to as FFT) 203, a P / S conversion circuit 204, and a symbol demapper 205 for performing a predetermined demodulation process are sequentially connected and configured.

FIG. 5 is a diagram showing a spectrum of a signal output from the symbol mapper 101. This example shows a spectrum when an OFDM signal using n carrier waves is generated, and each spectrum is arranged so as to overlap with a part of an adjacent spectrum in order to increase frequency use efficiency.

FIG. 6 is a diagram showing an example of an OFDM signal (a signal in which 16 carrier waves are multiplexed) output from the transmitting side P / S conversion circuit 104 when 16 (n = 15) carrier waves are used. It is.

The operation of the power line communication device shown in FIG. 4 will be described below with reference to FIGS. 5 and 6. First, as an operation of the transmission system, the symbol mapper 101 disperses transmission data into a plurality of carriers having frequency components as shown in FIG. 5 and orthogonal to each other and a predetermined modulated signal (for example, quadrature amplitude modulation (QAM) Alternatively, when phase modulation (PSK) is generated and output, the S / P conversion circuit 102 converts this into a parallel signal.

[0010] The modulated signal is not guaranteed to have the correct orthogonality due to a shift in the generation timing (phase shift) of each carrier, but each carrier is converted into a signal in the time domain by the IFFT transformer 103. Therefore, it is known that the above-mentioned shift in the occurrence timing is corrected.
The signal is output as a multiplexed waveform as shown in FIG. This OFDM signal is converted back to a serial signal by the P / S conversion circuit 104, processed into a signal that is hardly affected by multipath by the transmission side guard interval circuit 105, and the D / A converter 110 and the low-pass filter 120 Is converted to an analog signal from which harmonics have been removed via the IF / RF processing unit 1
After a predetermined process is performed in 30, it is transmitted to the transmission path.

On the other hand, as the operation of the receiving system, the IF / RF processing unit 1
When an OFDM signal converted to a digital signal after unnecessary processing is removed after predetermined processing via the 30 and the anti-aliasing filter 140 and the A / D converter 150 is input to the OFDM demodulation unit 200,
The guard interval processing on the transmission side is canceled by the guard interval circuit 201 on the reception side, and is converted into a parallel signal by the S / P conversion circuit 202 and supplied to the FFT 203. FFT203
Generates a plurality of orthogonal carriers (modulated signals) as frequency components from this signal and supplies them to a symbol demapper 205 via a P / S converter 204, where the transmission data is reproduced from the modulated signal. For this purpose, a predetermined demodulation process is performed.

As shown in FIG. 5, in the OFDM signal, since a part of the spectrum of each carrier overlaps with an adjacent spectrum, each carrier cannot be extracted (separated) by a filter. However, as is well known, signals can be separated by using orthogonality between carriers.
The description of this will be omitted because the description is complicated.
(See pp. 37-41 of the above document).

As described above, since the OFDM signal transmits one channel signal using a plurality of carriers, even if data of a specific carrier is lost due to noise, the possibility that data of the entire carrier is lost is low. Therefore, information data can be transmitted / received by using a predetermined error correction technique or the like even when the power line is used as a transmission line.

Japanese Patent Application Laid-Open No. 2000-165304 discloses that in a power line communication apparatus using a multicarrier system, a reception SN
For R, there is a description regarding selection of a modulation method that increases transmission rate and reliability, or selection of a carrier. Also,
Japanese Patent Application Laid-Open No. 2000-216752 describes that in a multicarrier communication apparatus, only a carrier other than a band that is greatly affected by noise is used. However, the above publication does not disclose specific noise evaluation means or SNR evaluation means relating to these devices (transmission paths).

[0015]

The above-described conventional power line communication apparatus has the following problems. In other words, a power line used as a transmission line generates noise whose level and frequency distribution change variously depending on the type of electronic device connected thereto, the number of connections, the state of use, and the state of laying the power line. Therefore, a carrier using a frequency with a high SNR characteristic (low noise level) can realize good communication with a small information transmission error, but a carrier using a frequency with a low SNR characteristic (high noise level),
There has been a problem that information transmission errors frequently occur due to noise and communication quality deteriorates. In the worst case, communication becomes impossible, and there is a problem that transmission power is wasted. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems related to the conventional power line communication apparatus, and it is an object of the present invention to improve communication quality based on SNR estimation related to a power line or to reduce waste of transmission power. It is intended to provide a device.

[0016]

According to a first aspect of the present invention, there is provided a power line communication apparatus according to the present invention, wherein at least a transmission system transmits transmission data orthogonally while partially overlapping each frequency component. A symbol mapper that generates a predetermined modulated signal based on a plurality of modulation schemes dispersed in a plurality of carrier waves, and an inverse Fourier transform unit that multiplexes the modulated signal in a time domain and outputs an OFDM signal, A power line communication device including a Fourier transform unit that generates the plurality of orthogonal carriers from a received OFDM signal as a receiving system, and a symbol demapper that performs a predetermined demodulation process, wherein the output of the Fourier transform unit is output for each carrier. Sampling a plurality of received signals in the average signal (S) and the noise component represented as a difference between the average signal (S) and each of the received signals From dispersion characteristics seeking noise power (N) estimates the SNR, and to perform the required communication control based on this result. The power line communication device according to claim 2 of the power line communication device according to the present invention, in the power line communication device according to claim 1, the transmission rate of transmission data from the plurality of modulation schemes for each carrier based on the SNR estimated value is optimal. The communication control is performed so as to select a different modulation method. The invention according to claim 3 of the power line communication device according to the present invention is the power line communication device according to claim 1 or 2, wherein the communication is performed so as not to use the carrier when the SNR estimated value is lower than a predetermined value. Control is performed.
The power line communication device according to claim 4 of the present invention is the power line communication device according to claim 1, 2, or 3, wherein the same data is transmitted to a predetermined number of carriers as a transmission system based on the SNR estimated value. , And in the receiving system, the communication control is performed so as to select a carrier wave having the maximum reception level from these. Claim 5 of the power line communication apparatus according to the present invention is a symbol for generating a predetermined modulated signal by dispersing transmission data as a transmission system to a plurality of orthogonal carrier waves while each frequency component partially overlaps A mapper, and an inverse Fourier transform unit that multiplexes the modulated signal in a time domain and outputs an OFDM signal, and a Fourier transform unit that generates the plurality of orthogonal carriers from a received OFDM signal as a receiving system, A power line communication device comprising a symbol demapper for performing demodulation processing, wherein a transmission system allocates the same data to a predetermined number of carrier waves and a reception system selects a carrier wave having a maximum reception level from among them. Control is performed. The invention according to claim 6 of the power line communication device according to the present invention is the power line carrier according to claim 5, wherein a plurality of received signals are sampled at an output of the Fourier transform means for each carrier, and an average signal (S ) And the average signal (S) and the noise power represented by the difference between the received signal and the noise component (N) is determined from the dispersion characteristic of the noise component to estimate the SNR. Can be selected.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 1 is a functional block diagram showing an embodiment of a power line communication device according to the present invention. The power line communication device shown in this example has an OF as a transmission system.
The DM modulator 10 is connected to a D / A converter (Digital / Analog converter) 30 and a low-pass filter 40 to output an intermediate frequency / high frequency
(Hereinafter, referred to as an IF / RF processing unit) 50, and the IF / RF processing unit 50 as a receiving system includes an anti-aliasing filter (low-pass filter) 60 and an A / D converter (analog / digital converter) 70. And is connected to the OFDM demodulation unit 20 via the.

The OFDM modulation unit 10 disperses transmission data into a plurality of orthogonal carrier waves with each frequency component partially overlapping and generates a predetermined modulated signal from a plurality of modulation schemes. Convert to parallel data
An S / P conversion circuit 12 and an inverse fast Fourier transform (IFF) as an inverse Fourier transform means
T) 13, a P / S conversion circuit 14 for converting parallel data to serial data, and a transmission-side guard interval circuit 15 for reducing the effects of multipath due to reflected waves from the transmission line (power line) branch. Connected and configured.

The OFDM demodulation unit 20 obtains a demodulated signal by the inverse operation of the above-described OFDM modulation unit 10, so that the reception side guard interval circuit 21, the S / P conversion circuit 22, and the orthogonalized OFDM signal are obtained from the received OFDM signal. Fast Fourier Transformer (Fast Fourier Tran) as Fourier Transform Means for Generating Multiple Carriers
sform, FFT) 23, a P / S conversion circuit 24, and a symbol demapper 25 that performs a predetermined demodulation process are sequentially connected, and an SNR characteristic related to a transmission path (power line) is estimated at a subsequent stage of the FFT 23. And a modulation scheme / carrier control section 27 for selecting a modulation scheme in the symbol mapper 11 and the symbol demapper 25 or a carrier to be used based on the estimation result.

The basic operation of the power line communication device including the OFDM modulation / demodulation unit is the same as that of the above-described prior art, and therefore the description is omitted.

A feature of the present invention is that the SNR estimating unit 26 estimates the SNR characteristic of the power line, and based on the estimated value, a plurality of modulation schemes (for example, PSK / QPSK / 8PSK / 1
6PSK) to select the best method
1 and the symbol demapper 25 are modulated by the modulation method / carrier control unit 27.
The point is to control via.

That is, BPSK (binary PS) used as a modulation method
K) / QPSK (4-level PSK) / 8PSK (8-level PSK) / 16PSK (16-level PSK) means that the number of information bits that can be transmitted by one symbol is 1/2/3 /
4 bits. Here, the more the number of information bits can be transmitted, the more the signal interval (PSK) on the signal space diagram
In the system, the phase shift interval) becomes narrow. For example, the phase shift interval of BPSK is 180 °, 90 ° for QPSK, and 45 ° for 8PSK, and the more information bits can be transmitted, the more the signal error due to noise is likely to occur, and a predetermined communication quality is obtained accordingly. Therefore, a high SNR characteristic (low noise characteristic) is required. On the other hand, BPSK cannot transmit more information bits per symbol, but the phase shift interval is as large as 180 ° and transmission errors due to noise are small, so that even low SNR characteristics do not affect communication quality.

Therefore, based on the above SNR estimation value, BPSK with a small number of information bits that can be transmitted but with a small transmission error is used for a carrier with a low SNR value, and 16PSK with a large number of transmission information bits with a carrier with a high SNR value is used. Select to improve the transmission rate.

When the SNR estimation unit 26 estimates that the SNR value of the carrier is smaller than a predetermined value, the communication quality deteriorates and communication becomes impossible. In this case, waste of transmission power is improved. Modulation method so that this carrier is turned off.
The symbol mapper 11 is controlled via the carrier control unit 27.

Next, the SNR estimation in the SNR estimator 26 will be described in detail. FIG. 2 is a diagram for explaining the principle of SNR estimation used in the power line communication device according to the present invention. In this SNR estimation, first, as shown in FIG. 2, a plurality of data of about 100 points are sampled from a reception signal output from the FFT 23 for each carrier, and these are decomposed into I and Q components to obtain a reception signal vector. r1, r2, r3
·············· Thereafter, an average value of each of the I component and the Q component of all the sampled received signal vectors is obtained, and this is set as an average signal vector (S). Further, a difference between the average signal vector (S) and each received signal vector is obtained, and this is displayed as a noise component as n1, n2, n3,.... If 100 points are taken as sampling data, r1, r2,..., R100 are obtained as noise components, and when this standard deviation (σ) is obtained, it becomes a broken line circle in the figure.

Generally, noise can be treated as a Gaussian probability distribution, and it is known that the square of the standard deviation (σ) becomes the noise power (N). By taking the ratio between S) and this noise power (N), the SNR relating to the transmission path (power line) can be estimated.

As described above, since the power line communication apparatus according to the present invention operates, it is possible to select an optimal modulation method according to the SNR characteristics of each carrier, thereby improving the deterioration of communication quality. In addition, since a carrier that cannot be used for communication is not used from the beginning, useless transmission power consumption can be prevented.

Next, the second embodiment of the power line communication apparatus according to the present invention will be described.
A second embodiment will be described. FIG. 3 is a functional block diagram showing a second embodiment of the power line communication device according to the present invention. The power line communication device shown in this figure is obtained by replacing the modulation method / carrier control unit 27 in the first embodiment shown in FIG. 1 with a diversity control unit.

The basic operation of the power line communication device shown in this figure is the same as that of the first embodiment, except for the following points. That is, when the variation range of the SNR value estimated by the SNR estimating unit 26 exceeds a predetermined value, the symbol mapper 11 and the symbol demapper 25 are controlled via the diversity control unit 27 as follows. First, in the symbol mapper 11, the same data is assigned to a predetermined number of carriers, for example, two carriers. Therefore, among the carrier waves output from the symbol mapper 11 shown in FIG. 5, the same data is allocated to, for example, f0 and f1, f2 and f3,... Further, when receiving such data, the symbol demapper compares the amplitude levels of the carriers to which the same data is assigned, and employs the signal of the higher-level carrier as the reception data.

By making the power line communication device according to the present invention function as described above, a diversity effect can be obtained. Therefore, when the SNR value fluctuates greatly, for example, when the transmission path is multipath due to a reflected wave from the power line branch. Therefore, it is possible to obtain a relatively stable communication quality even if a fading state is caused.

In the second embodiment, the above-described diversity control is performed based on the fluctuation state of the SNR estimation value. However, since the transmission state of the power line is generally extremely poor, the SNR estimation It is not necessary to particularly explain that the diversity control is effective from the beginning regardless of the value.

As described above, since the power line communication apparatus according to the present invention shown as the second embodiment operates, it is possible to perform stable communication due to the diversity effect even when the transmission path is in a fading state or the like. .

Although the SNR estimation in each of the first and second embodiments described above is usually performed using the training signal at the start of communication, the head (header) of the communication frame is used even during communication. It is possible to do
The required control described above can be performed during communication. Also, when performing the above-described modulation scheme control, carrier OFF control, or diversity control based on the SNR information obtained on the receiving side, it is necessary to report information related to this to the transmission partner apparatus. The above training signal,
What is necessary is just to use the frame head (header part).

[0034]

As described above, according to the present invention, the SNR characteristic of the transmission path is estimated and the optimum modulation method is selected for each carrier, so that the deterioration of the communication quality can be improved.
Further, since the carrier wave that cannot be communicated is not used from the beginning, it is very effective in realizing a power line communication device that can reduce waste of transmission power. Furthermore, by performing diversity control, stable communication can be performed even when the transmission path is in a fading state.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a first embodiment of a power line communication device according to the present invention.

FIG. 2 shows S used in the power line communication device according to the present invention.
Diagram explaining the principle of NR estimation

FIG. 3 is a functional block diagram illustrating a power line communication apparatus according to a second embodiment of the present invention.

FIG. 4 is a functional block diagram illustrating a configuration example of a conventional power line communication device using the OFDM method.

FIG. 5 illustrates a spectrum of an OFDM signal.

FIG. 6 is a schematic diagram showing a multiplexed waveform of an OFDM signal using 16 carriers.

[Explanation of symbols]

 10.OFDM modulation section 20 OFDM demodulation section 30 D / A converter (digital / analog converter) 40 low-pass filter 50 intermediate frequency high frequency processing section 60 A / D converter (analog / digital converter)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K004 AA06 GB02 GC06 GC11 5K022 DD01 DD23 DD33 5K046 AA03 PP01 PS03 PS05 PS46 PS51 PS52

Claims (6)

[Claims] 1. A symbol mapper for distributing transmission data into a plurality of orthogonal carrier waves with at least some frequency components overlapping at least as a transmission system and generating a predetermined modulated signal based on a plurality of modulation schemes, With an inverse Fourier transform means for multiplexing the modulated signal in the time domain and outputting an OFDM signal, and a Fourier transform means for generating the plurality of orthogonal carriers from the received OFDM signal as a receiving system,
A power line communication device comprising a symbol demapper for performing a predetermined demodulation process, wherein a plurality of received signals are sampled at an output of the Fourier transform means for each carrier wave, and an average signal (S) and the average signal (S Power line communication apparatus, wherein noise power (N) is obtained from a dispersion characteristic of a noise component expressed as a difference between the received signal and the received signal to estimate SNR, and a required communication control is performed based on the result. . 2. The communication control according to claim 1, wherein the communication control is performed so as to select a modulation scheme that optimizes a transmission rate of transmission data from the plurality of modulation schemes for each carrier based on the SNR estimation value. A power line communication device according to claim 1. 3. The power line communication device according to claim 1, wherein the communication control is performed such that the carrier is not used when the estimated SNR value is lower than a predetermined value. 4. The communication system according to claim 2, wherein the same data is allocated to a predetermined number of carriers as a transmission system based on the SNR estimation value, and the reception system performs the communication control so as to select a carrier having a maximum reception level from among them. Claims characterized by the following:
4. The power line communication device according to claim 1, 2 or 3. 5. A symbol mapper for generating a predetermined modulated signal by dispersing transmission data at least as a transmission system into a plurality of orthogonal carrier waves with each frequency component partially overlapping,
An inverse Fourier transform unit that multiplexes the modulated signal in the time domain and outputs an OFDM signal, and a Fourier transform unit that generates the plurality of orthogonal carriers from a received OFDM signal as a receiving system, and a predetermined demodulation process. And a symbol demapper for performing a diversity control for allocating the same data to a predetermined number of carriers as a transmission system and selecting a carrier having a maximum reception level from among them in a reception system. A power line communication device characterized by the above-mentioned. 6. A plurality of received signals are sampled at the output of the Fourier transform means for each carrier wave, and an average signal (S) and noise represented as a difference between the average signal (S) and each of the received signals are sampled. 6. The power line communication device according to claim 5, wherein the noise power (N) is obtained from the dispersion characteristics of the components to estimate the SNR, and it is possible to select whether or not to perform the diversity control based on the result.