JP2008141224A - Diversity reception method and reception apparatus in wired communication - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform diversity reception using current and voltage at the reception end of information transmission signals in wired communication. <P>SOLUTION: A current signal ir(t) and a voltage signal vr(t) of a pair of lines, such as power lines or telephone lines are detected at the reception end of the pair of lines. A combining/equalizing part 6 multiples a current signal Ir(k) and a voltage signal Vr(k) which are each Fourier transformed, by weight coefficients gi(k) and gv(k), respectively, and then adds the multiplication results together. The weight coefficients gi(k) and gv(k) are determined such that the S/N of a signal obtained by that addition is maximized. The complementary relationship between the current and the voltage can be utilized to improve the reception quality. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a diversity receiving method and a receiving apparatus that improve reception quality when communication is performed using a transmission line such as a power line or a telephone line.

The diversity reception method is a method for improving reception quality by receiving a plurality of reception signals having the same content and combining them or selecting a higher quality signal.
Diversity reception methods are conventionally used in the field of wireless communications for signals received at different antennas, signals with different polarizations, signals with different radio wave arrival angles (diversity target signals are called diversity branches), etc. This has been done to improve the quality of the received signal.

The idea of diversity reception is also adopted in wired communication (see Patent Documents 1 and 2).
Patent Documents 1 and 2 propose a method for diversity reception of a communication signal at a receiving end via a plurality of power lines through which the same communication signal is transmitted.
JP 2004-64405 A Japanese Patent Laid-Open No. 11-205201

However, the diversity reception methods described in Patent Documents 1 and 2 use a plurality of lines.
For this reason, it is necessary to lay a plurality of lines between the transmission end and the reception end, and there is a problem that the cost for constructing the communication system increases.
Generally, in order to obtain the reception quality improvement effect by diversity, it is necessary that the correlation between the diversity branches is small. That is, it is necessary to have a complementary relationship in which one is in a bad state (eg, the amplitude is small) and the other is not bad (eg, the amplitude is large).

The inventor has noted that the relationship between the current flowing through the pair of lines and the voltage is complementary.
That is, when the impedance of the load connected to the line is large, the voltage of the load increases and the current decreases. When the load impedance is small, the load voltage decreases and the current increases.

Therefore, since the current and the voltage have a complementary relationship at the receiving end of the information transmission signal, if these are selected as the diversity branch, an effect of improving the reception quality can be expected.
An object of the present invention is to provide a diversity receiving method and a receiving apparatus capable of improving reception quality by using currents and voltages having a complementary relationship at the receiving end of an information transmission signal in wired communication. To do.

  The diversity reception method of the present invention detects and detects the voltage and current of the line at the receiving end of the line when the information transmission signal is communicated by being superimposed on a pair of lines such as a power line and a telephone line. In this method, diversity transmission is performed by selecting an information transmission signal (referred to as a voltage signal) included in the detected voltage and an information transmission signal (referred to as a current signal) included in the detected current as a diversity branch (claim 1).

By this method, it is possible to expect an effect of improving reception quality by utilizing a complementary relationship between current and voltage.
The diversity reception may employ so-called combining diversity in which the detected current signal and voltage signal are weighted and combined so as to obtain the best reception quality (claim 2). You may employ | adopt what is called selection diversity which selects the better reception quality among a voltage signal and a current signal (Claim 5).

  In the synthesis process, the detected voltage signal and current signal may be Fourier transformed, and the Fourier transformed frequency domain signals may be weighted and synthesized. In particular, when transmitting a broadband information transmission signal, the frequency characteristics of the load impedance are generally not uniform, and large and small fluctuations occur within the signal band. According to this method, in the frequency domain, the complementary current signal and voltage signal can be combined to improve the non-uniformity of the signal spectrum within the band.

In particular, if one of the voltage signal and the current signal is a real part and the other is an imaginary part to create a complex time signal and Fourier transform (Claim 4), the voltage signal and the current signal are individually obtained. Compared with the Fourier transform, the number of Fourier transform circuits can be halved and the circuit configuration of the Fourier transform circuit is simplified.
As an information transmission signal transmission system related to the Fourier transform, there are an OFDM system (Claim 6) and a single carrier block transmission system (Claim 7).

The line is, for example, a power line or a telephone line (Claim 8). When a power line is used as a line, the load impedance of an electric device connected to the line fluctuates with time depending on the power on / off of the device. Also, when the line is a telephone line, the load impedance varies depending on the on-hook and off-hook of the telephone connected to the line, so that the present invention can be effectively applied.
The diversity receiver of the present invention receives an information transmission signal superimposed on a pair of lines, an information transmission signal (referred to as a current signal) obtained by detecting the current of the line, A diversity receiver is provided for diversity-receiving an information transmission signal (referred to as a voltage signal) obtained by detecting the voltage.

With this receiving apparatus, it is possible to expect an effect of improving reception quality by utilizing a complementary relationship between current and voltage.
The current signal can be obtained through a current detector that detects a current at the receiving end of the line, and the voltage signal can be obtained through a voltage detector that detects a voltage at the receiving end of the line. 10). According to this configuration, a current signal and a voltage signal can be obtained without installing a current detection unit and a voltage detection unit inside the reception device, and the reception device can be downsized.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram illustrating a detection circuit for an information transmission signal at a power receiving end of a power line or a telephone line when communication is performed by superimposing the information transmission signal on a pair of power lines or a telephone line.
The power line may be a transmission / distribution line that supplies commercial power to a home or office, or an in-vehicle wiring that supplies DC power to the vehicle.

The information transmission signal may be either a baseband encoded signal such as an RZ code or a Manchester code, or a band signal obtained by performing digital modulation such as PSK, FSK, or QAM.
The information transmission signal is detected as a current signal by the current component detection circuit 1 and detected as a voltage signal by the voltage component detection circuit 2.

For example, a current signal can be easily detected as the voltage across a resistor inserted in series with the line, but if a resistor is inserted, a loss occurs, so a coil (current transformer) surrounding the line is generally inserted. . Here, as one type of current transformer, a current probe is used that detects the voltage generated in the winding by inserting a power line into the magnetic circuit of the transformer.
The voltage signal only needs to detect the voltage generated between the lines at the power receiving end, and the circuit configuration for the detection is arbitrary.

It should be noted that the current signal itself does not necessarily have to be expressed as a current change, and may be converted into a voltage by a resistor or the like. Hereinafter, in the embodiment of the present invention, description will be made assuming that both the current signal and the voltage signal are signals represented by voltage changes.
In the diversity reception method of the present invention, these current signals and voltage signals are handled as diversity branches, and the reception quality is improved by combining these voltage signals and current signals or by selecting one of them.

Since the frequency band of the detected voltage signal and current signal is higher than the power line power frequency of the power line and the telephone signal frequency of the telephone line, in order to remove the low frequency power supply voltage / current and telephone signal. It is desirable to pass through the high-pass filter F.
FIG. 2 is a circuit block diagram when the high-pass filter F is used for each of the current component detection circuit 1 and the voltage component detection circuit 2. The form of the high-pass filter F is arbitrary such as a circuit using a resistor and a capacitor and a circuit using a coil and a capacitor.

Hereinafter, these detected current signals are denoted by ir (t) and voltage signals are denoted by vr (t).
The diversity method includes “combined diversity” in which a predetermined weighting factor is added to each of the current signal ir (t) and the voltage signal vr (t) so as to obtain the best communication quality, and the current signal ir (t), There is “selection diversity” in which one of the voltage signals vr (t) having the better communication quality is selected. “Communication quality is good” means, for example, a higher received power, a higher SN ratio, or a lower transmission distortion. In addition, there is a type of selection diversity in which the selection switching circuit is installed in the pre-demodulation stage or the post-demodulation stage.

The following embodiments will be described in detail by taking synthetic diversity as an example.
FIG. 3 is a block diagram illustrating an OFDM (Orthogonal Frequency Division Multiplex) scheme combining diversity receiver.
The combined diversity receiver inputs a current signal ir (t) and a voltage signal vr (t). The current signal ir (t) is converted into 2N parallel signals through the serial-parallel conversion circuit 4a that parallelizes the serialized signal every N symbols (N is 256, for example). The voltage signal vr (t) also passes through the N symbol serial / parallel conversion circuit 4b and becomes 2N parallel signals. “2” is added because the input / output of the IFFT (Inverse Fourier Transform) circuit is a complex number, and thus has an imaginary part as well as a real part. However, since the current signal ir (t) and the voltage signal vr (t) are real signals, the values of the imaginary part are all zero.

Each parallel signal is Fourier transformed by FFT circuits 5a and 5b. The Fourier-transformed signal is expressed as Ir (k), Vr (k). Here, “k” is a variable representing a discrete frequency, and k = 0, 1, 2,..., N−1.
On the other hand, the transmission path characteristics of the current signal ir (t) and the voltage signal vr (t) are estimated by the transmission path characteristics estimation sections 8a and 8b, respectively. The transmission path characteristic is a transfer function from the transmission end to the reception end of the line. For example, it can be obtained by extracting a pilot signal inserted in advance in the information transmission signal with a filter and measuring its strength and phase.

The transmission path characteristic estimators 8a and 8b output the transfer function in the frequency domain for the current signal Ir (k) and the voltage signal Vr (k). These signals are a total of 2N parallel signals of a real part and an imaginary part expressed by the same discrete frequency as the discrete frequency k, and are represented as hi (k) and hv (k), respectively.
The synthesis equalization unit 6 multiplies the weighted coefficients gi (k) and gv (k) by the signals Ir (k) and Vr (k) after each Fourier transform and adds them. The added signal R (k) is expressed as follows.

R (k) = gi (k) Ir (k) + gv (k) Vr (k)
The synthesis equalization unit 6 determines the weighting factors gi (k) and gv (k) so as to maximize the SN ratio of the signal R (k) after the addition. The weighting factors gi (k) and gv (k) are calculated using the hi (k) and hv (k).
gi (k) = h ^* i (k) / (| h ^* i (k) | ² + | h ^* v (k) | ² )
gv (k) = h ^* v (k) / (| h ^* i (k) | ² + | h ^* v (k) | ² )
Can be calculated. “*” Represents a complex conjugate.

Note that details of how to obtain the weighting factors gi (k) and gv (k) are examples of antenna diversity, but the Trikes Planning Department, "~ OFDM modulation technology for digital broadcasting / mobile communications" p.115. -See p.120, Trikes, Inc., issued March 6, 2000.
As a result, the error rate of the demodulated signal can be minimized.
Although the above transmission path characteristic estimation units 8a and 8b have determined the transmission path characteristics hi (k) and hv (k) using the pilot signal, other transmission path characteristics may be used. For example, a known symbol instead of a transmitted data symbol that inserts a known signal (such as a chirp signal or PN sequence) at appropriate intervals and measures the distortion at the receiver to estimate the channel characteristics. There is a method of estimating the transmission line characteristics by transmitting the signal at regular intervals and measuring the distortion. For details, see the above-mentioned document p.102-p.108.

The synthesis equalization unit 6 determines the weighting factors gi (k) and gv (k) so that the signal-to-noise ratio of the signal R (k) is maximized. Can be set, and the determination method is arbitrary.
The signal R (k) added by the synthesis equalization unit 6 enters the demodulator 7 and is converted into the original code string. The code string is parallel-serial converted by the N symbol parallel-serial conversion circuit 10 and extracted as information data.

As described above, this combining diversity receiver detects the current signal and voltage signal at the receiving end of the power line or telephone line, and combines the current signal and voltage signal with a predetermined weight so that the transmission characteristics are the best. Therefore, the best information transmission signal can be restored at any time.
Next, a case of a single carrier block transmission system (Single Carrier Block Transmission, SCBT, hereinafter referred to as SCBT system) will be described.

The SCBT scheme is a block transmission scheme in which a signal block composed of a plurality of information symbols is transmitted and equalization or demodulation processing is performed in units of blocks on the receiving side. GI), and a transmission method for performing discrete frequency domain equalization on the receiving side.
Here, the information transmission signal is a baseband signal for transmitting information symbols in a single frequency band, or a band signal obtained by modulating a single carrier.

As a guard interval, a copy of the transmission block tail part (cyclic prefix) inserted is called SC-CP (Single carrier block transmission with cyclic prefix) method, and it is effective by using discrete Fourier transform on the receiving side. Frequency domain equalization can be performed. For details, see 2004 Microwave Workshop Digest, p.523-532.
FIG. 4 is a block diagram showing an SCBT method diversity receiver in wired communication.

  The difference between the SCBT method and the OFDM method is that, in the OFDM method, the information transmission signal is subjected to inverse Fourier transform on the transmission side and sent to the transmission line, and the receiver performs Fourier transform, equalization and use of the signal. In the SCBT system, the transmitter sends out the signal to the transmission line without performing the inverse Fourier transform, the receiver performs the Fourier transform, equalizes in the frequency domain, and uses the inverse Fourier transform. From the viewpoint of the transmission signal spectrum, OFDM is a multi-carrier and SCBT is a single carrier.

Since the reception time signal is subjected to discrete Fourier transform on the SCBT receiver side, the contents of the present invention described above can be applied. Therefore, the SCBT type N-symbol serial / parallel conversion circuits 4a and 4b, the FFT circuit 5, the transmission path characteristic estimation units 8a and 8b, and the synthesis equalization unit 6 are substantially the same circuits as the OFDM type circuits.
In FIG. 4, the signal R (k) synthesized by the synthesis equalization unit 6 is inverse Fourier transformed by the IFFT circuit 9 and transformed into a symbol string on the time axis. The symbol string is serially converted into N symbols, demodulated by a demodulator 7, and extracted as information data.

As described above, the SCBT system diversity receiver can restore the best information transmission signal at any point in time as in the case of the OFDM system diversity receiver.
Next, a simplified combining diversity system will be described in which one of the current signal ir (t) and the voltage signal vr (t) is regarded as a real part and the other is regarded as an imaginary part.

In the circuits of FIGS. 3 and 4, the current signal ir (t) is represented by 2N parallel complex signals, of which N in the imaginary part is 0, and actually, N in the real part are required. . The voltage signal vr (t) is also expressed by 2N parallel complex signals, of which N in the imaginary part is 0, and what is actually required is N in the real part. Therefore, the FFT circuits 5a and 5b have redundant circuit configurations.
The simplified combining diversity type FFT circuit 5 is shown in FIG. The FFT circuit 5 includes a real part of a current signal ir (t) that is N parallel signals and a real part of a voltage signal vr (t) that is N parallel signals multiplied by an imaginary unit j. Sum u (t) = ir (t) + jvr (t)
Is the input signal. The input signal u (t) is Fourier-transformed, and a frequency domain signal U (k) = X (k) + jZ (k) is obtained at the output of the FFT circuit 5. Here, X (k) and Z (k) are the real part and imaginary part of U (k), respectively. Since X (k) and Z (k) are not Fourier transform values of desired current and voltage signals, they are converted into Fourier transform values Ir (k) and Vr (k) of current and voltage signals by the following calculation.

Ir (k) = [X (k) / 2 + X (Nk) / 2] + j [Z (k) / 2−Z (nk) / 2] (1)
Vr (k) = [Z (k) / 2 + Z (Nk) / 2] -j [X (k) / 2-X (nk) / 2] (2)
Where N is the number of samples in the time domain, that is, the number of FFT points, n = 0,..., N−1 (Miyakawa, Imai “Fast Fourier Transform” p.185-p.187, Science and Technology Publishers Issued December 15, 1978).
By this calculation, the Fourier transform value Ir (k) of the current signal and the Fourier transform value Vr (k) of the voltage signal can be separated from the output value of the FFT circuit 5.

Ir (k) and Vr (k) thus separated are input to the synthesis equalization unit 6. The following processing is the same as that described in FIG.
This simplified combining diversity system has an advantage that only one FFT circuit 5 is required unlike the circuits of FIGS. That is, in the circuits shown in FIGS. 3 and 4, only two FFT circuits are actually processed while using two FFT circuits 5a and 5b. However, in the circuit shown in FIG. 5, one complex time signal is composed of the N parallel signals, ie, the current signal ir (t) and the voltage signal vr (t). Can be used to process. The separation of the Fourier transform value Ir (k) of the current signal and the Fourier transform value Vr (k) of the voltage signal from the output of the FFT circuit 5 can be realized by simple four arithmetic operations. Therefore, the circuit scale of the entire FFT can be halved, the receiving apparatus can be simplified, and the same diversity effect as when the two FFT circuits are used can be obtained.

FIG. 6 is a block diagram showing a simplified combining diversity receiving apparatus of the OFDM method.
The difference between the simplified combining diversity receiving apparatus and the combining diversity receiving apparatus of FIG. 3 is that the current signal ir (t) passes through the N-symbol serial / parallel conversion circuit 14a and the N imaginary part 0 is omitted. The voltage signal vr (t) also becomes N parallel signals through the N symbol serial / parallel conversion circuit 14b. "2" is not attached.

Unlike FIG. 3, the FFT circuit 5 includes a complexing unit 51, an FFT unit 52, and a calculation unit 53.
The complexing unit 51 uses the N parallel real signals corresponding to the current signal ir (t) and the N parallel real signals corresponding to the voltage signal vr (t) to generate a complex time signal u ( t) = ir (t) + jvr (t)
make.

The FFT unit 52 performs a Fourier transform on this signal, and outputs a complex signal U (k) in the frequency domain.
The calculation unit 53 obtains Ir (k) and Vr (k) using the above-described equations (1) and (2).
As described above, the synthesis equalization unit 6 determines the weighting factors gi (k) and gv (k), multiplies the signals Ir (k) and Vr (k) after each Fourier transform, and adds them. The added signal R (k) is expressed as follows.

R (k) = gi (k) Ir (k) + gv (k) Vr (k)
The synthesis equalization unit 6 determines the weighting factors gi (k) and gv (k) so as to maximize the SN ratio of the signal R (k) after the addition. The demodulator 7 converts the signal R (k) into the original code string, and the code string is N-serial converted in parallel and extracted as information data.
FIG. 7 is a block diagram showing a simplified combining diversity receiver of the SCBT method.

The difference from the SCBT system diversity receiver of FIG. 4 is that the current signal ir (t) passes through the N symbol serial / parallel conversion circuit 14a to become N parallel signals with the imaginary part 0 omitted, and the voltage signal vr (t) also means that N parallel signals pass through the N symbol serial / parallel conversion circuit 14b.
Unlike FIG. 4, the FFT circuit 5 includes a complexing unit 51, an FFT unit 52, and a calculation unit 53.

The complexing unit 51 uses the N parallel real signals corresponding to the current signal ir (t) and the N parallel real signals corresponding to the voltage signal vr (t) to generate a complex time signal u (t). = Ir (t) + jvr (t)
The FFT unit 52 performs Fourier transform on this function, and the calculation unit 53 obtains Ir (k) and Vr (k) using the above-described equations (1) and (2). The functions of the other synthesis equalization unit 6 and IFFT circuit 9 are the same as those in FIG. As described above, even with the simplified combining diversity receiving apparatus of the OFDM system and the SCBT system, it is possible to obtain the same diversity effect as in the case where the two FFT circuits are used.

  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. For example, a receiving apparatus including a current detection unit and a voltage detection unit together with a diversity reception unit. It is good. In addition, various modifications can be made within the scope of the present invention.

It is a block diagram which shows the detection circuit of the information transmission signal in a power receiving end in the case of communicating by superimposing an information transmission signal on a pair of power lines or telephone lines. FIG. 4 is a circuit block diagram when a high-pass filter F is used for each of the current component detection circuit 1 and the voltage component detection circuit 2. It is a block diagram which shows the synthetic | combination diversity receiver of an OFDM system. It is a block diagram which shows the synthetic | combination diversity receiver of a SCBT system. FIG. 5 is a block diagram showing a simplified combining diversity type FFT circuit 5; It is a block diagram which shows the simplification synthetic | combination diversity receiver of an OFDM system. It is a block diagram which shows the simplification synthetic | combination diversity receiver of a SCBT system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Current component detection circuit 2 Voltage component detection circuit 3 Load 4a, 4b N symbol serial / parallel conversion circuit 5, 5a, 5b FFT circuit 6 Synthesis | combination equalization part 7 Demodulator 8a, 8b Transmission path characteristic estimation part 9 IFFT circuit 10 N symbol Parallel / serial conversion circuits 14a and 14b N symbol parallel / serial conversion circuit 51 Complexing unit 52 FFT unit 53 Operation unit

Claims (10)

In the method of communicating information transmission signals superimposed on a pair of lines,
Detecting the voltage and current of the line at the receiving end of the line,
A diversity reception method in wired communication, wherein diversity transmission is performed on an information transmission signal (referred to as a voltage signal) included in a detected voltage and an information transmission signal (referred to as a current signal) included in a detected current.   The diversity reception method in wired communication according to claim 1, wherein the diversity reception is performed by weighting and combining the detected current signal and voltage signal so that reception quality is best.   The diversity reception method in wired communication according to claim 2, wherein the detected voltage signal and current signal are each subjected to Fourier transform, and the Fourier transformed signals are weighted and combined.   4. The diversity reception method in wired communication according to claim 3, wherein one of the voltage signal and the current signal is a real part and the other is an imaginary part to create a complex time signal and perform Fourier transform.   The diversity reception method in wired communication according to claim 1, wherein the diversity reception is performed by selecting a voltage signal or a current signal having a better reception quality.   6. The diversity reception method in wired communication according to claim 2, wherein a transmission method of the information transmission signal is an OFDM (Orthogonal Frequency Division Multiplex) method.   The transmission method of the information transmission signal is a single carrier block transmission method in which a guard block is added to a signal block composed of a plurality of symbols for transmission, and discrete frequency domain equalization is performed on the receiving side. 6. A diversity receiving method in wired communication according to any one of 5 above.   The diversity reception method in wired communication according to claim 1, wherein the line is a power line or a telephone line. In an apparatus for receiving an information transmission signal superimposed on a pair of lines,
A diversity receiver that receives diversity transmission of an information transmission signal (referred to as current signal) obtained by detecting the current of the line and an information transmission signal (referred to as voltage signal) obtained by detecting the voltage of the line; A receiving device.   The reception according to claim 9, wherein the current signal is detected through a current detection unit that detects a current at a reception end of the line, and the voltage signal is detected through a voltage detection unit that detects a voltage at the reception end of the line. apparatus.

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