JPS6158338A - Spread spectrum phase encoding power communication system - Google Patents

Abstract

PURPOSE:To obtain high signal-to-noise ratio of received signal even under a peak power limiting condition by transmitting a narrow bankwidth information signal through multiplification modulation in a psuedo-random system and spectrum dispersion in a wide and and demodulating the received signal through correlation detection and spectrum inverse dispersion. CONSTITUTION:Signals 166(1)-166(N) on the terminal unit side are multiplexed (111) to be fed to a multiplying circuit 110. A signal 163 from a psuedo-random system series 109 and a clock 170 are fed to an exclusive OR gate 114, the output 171 of which is multiplied with a signal 166 of a circuit 110. The output of the circuit 110 is fed to a coupler 100 for attenuation of a low frequency component before being fed to a power transmission line. On the receiving side, the input signal from the power line is separated in a filter in a coupler 100 into commercial power and high frequency spectrum dispersion signal. The separated high frequency spectrum dispersion signal is fed to a synchronizing extractor 104, and a spectrum inverse diffusion demodulation 105 is effected through a psuedo-random series to obtain information signals 165(1)-165(N).

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a communication method for transmitting information signals via power lines.

(Prior Art and its Problems) Conventionally, various modulation methods have been used in communication methods for transmitting information signals via power lines depending on the type of transmission path. Single-sideband modulation was used for power transmission lines, and frequency modulation or phase modulation was used for distribution lines.

For example, iTriple E Transactions on Consumer Electronics? part one t
August 11982 jcE-28j number 3 (
IFiEE Transactions on Con
sumer Electronics p Part
Lt August 1982*'Vo1. CB-2
Mitchell Lee (8yNo, 3)
A New Carri
er Current Transceiver I
C) The method described in K is frequency shift key ink modulation (modulated to F8), which is a type of frequency modulation method. However, the transmission characteristics of power lines exhibit very poor transmission conditions such as large noise and fluctuations in transmission line characteristics due to load characteristics. Under such poor transmission environment, the patent application
A spread spectrum method as shown in the specification of No. 194908 is considered to be promising. However, there are restrictions on the signal frequency band that can be used for power line transmission, making it difficult to use low frequency and high frequency regions. Particularly in spread spectrum signals, waveform distortion due to low-frequency cutoff has a negative effect on the synchronization system, and transmission line codes with signal components down to very low frequencies, as shown in Japanese Patent Application No. 58-194908, are unstable. There was a possibility that synchronization could not be maintained. Furthermore, since the noise spectrum of a power line tends to be biased toward the low frequency region, it is desirable that the signal spectrum is small in the low frequency region from the viewpoint of signal-to-noise ratio (SN ratio).

(Object of the Invention) An object of the present invention is to eliminate the drawbacks of the above-mentioned conventional methods and provide a high-quality high-speed data transmission method via a power line.

(Structure of the Invention) According to the present invention, in a power line communication system that transmits an information signal via a power line, on the transmitting side, the information signal is spread spectrum modulated using a phase-encoded pseudo-random sequence, and then sent to the coupler. After the low frequency components are attenuated by a filter, they are sent to the power line, and on the receiving side, the input signal from the power line is separated into a commercial power signal and a high frequency spread spectrum signal by a filter using a coupler. A spread spectrum phase encoded power line communication system is obtained, which is characterized in that the high frequency spread spectrum signal is subjected to spectrum despread demodulation using a pseudorandom sequence that is phase encoded in the same manner as that on the transmitting side, thereby obtaining an information signal and performing communication. .

(Principle of the Invention) In the frequency spread communication system, a narrowband information signal is multiplied and modulated using a pseudo-random sequence with a high clock frequency to spread the spectrum over a wide band and then transmitted.The receiving side uses correlation detection to detect the received signal. This method demodulates the signal by despreading the spectrum and obtains a high reception 8N (signal-to-noise) ratio even under peak power limitations. An m-sequence (maximum length sequence) is often used as a pseudo-random sequence. Such frequency spread communication has been applied to wireless communication in the past because it is resistant to narrowband noise, resistant to transmission path fluctuations such as fading, and has high confidentiality.

Regarding application to wired communication, since the characteristics of wired lines are better than those of wireless lines, studies are being conducted on the scope of application with a focus on multiple access using code multiplexing. However, since power lines are originally intended for transmitting commercial power signals, there are almost no regulations regarding high frequency transmission characteristics. Therefore, as described above, the high frequency transmission characteristics vary greatly depending on the connection state of the electrical equipment, resulting in a poor high frequency line environment even though it is wired. Furthermore, the adverse effect on commercial power signals, which is the original purpose of the power line, must be kept to a minimum, and the high-frequency signal power must also be kept low to minimize the influence on electrical equipment.

As described above using the wireless link example, we have shown that the frequency spread communication method can perform good transmission in such a poor high-frequency line environment, but it is also important to minimize the impact on commercial power signals and electrical equipment. From this point of view, in spread spectrum communication, the modulation spectrum is spread over a wide band and in white, so the spectrum density is low and good characteristics are exhibited. Considering the above, it can be seen that applying the spread spectrum communication method to power line transmission is extremely useful and provides novel effects that could not be obtained with conventional methods. Furthermore, in the present invention, by phase-encoding the pseudorandom sequence,
Transmission path characteristics and constraints on the band used in power line transmission (transmission is possible from 101GIz to 4501GIz)
Let it be z. ) good transmission can be achieved under The principle of applying this phase encoding to spread spectrum power line communication will be explained with reference to the drawings. Here, there may be various types of phase encoding, but in the following explanation, Manchester encoding, which is known as a typical phase encoding method, will be explained. FIG. 5 shows the modulation process in the spread spectrum communication system. The modulation process in the spread spectrum communication system is shown in Figure 5 (a
) is multiplicatively modulated using a sequence (c) obtained by Manchester encoding a pseudorandom sequence generated at a high clock frequency as shown in FIG. It spreads the spectrum.

FIG. 5(d) shows an example of a signal waveform subjected to spread spectrum modulation.

FIG. 2 shows an example of a frequency spectrum of a signal in a spread spectrum modulation process. FIG. 2(a) is an example of the spectrum of a narrowband information signal, and FIG. 2(b) is an example of the spectrum of a Manchester encoded pseudorandom sequence. As is well known, the Manchester code is an example of Manchester coding because its signal spectrum has small low-frequency components. Note that FIG. 2(c) shows only the main rope of the modulated signal spectrum.

In the partial spectra 200(1) to 200(2N) in the spread spectrum in FIG. 2(c), the signal components of the narrowband information signal are distributed evenly in the signal band that can be sent to the power line. It can be seen that the low-frequency components, which are dispersed but cannot be used in the first place, have a small spectrum, and are shaped into a signal spectrum that matches the transmission path characteristics. Here, N indicates the period length of the pseudo-random sequence, and in the demodulation process, correlation detection is performed on the received signal using the same pseudo-random sequence as on the modulating side, and the spread signal having the spectrum shown in Fig. 2(c) is converted into a spread signal as shown in Fig. 2(c). A narrowband information signal having a spectrum of (, ) can be obtained.

The above-mentioned property that the narrowband information signal is spread almost evenly is that
This is especially effective for communication using power lines. The transmission characteristics of power lines vary greatly depending on load conditions, and may produce multiple zero points.

FIG. 3(,) shows an example of the transmission characteristics of a power line in a certain load state. The characteristics shown in FIG. 3 (,) are an example in which a transmission zero point occurs at the frequency position fl. Currently, f,
If the frequency is the center frequency, the received signal power will be extremely small and the transmission quality will be greatly degraded. on the other hand,
According to the spread spectrum power line communication system of the present invention, almost all the signal power is received due to the above-mentioned nature of the narrowband information signal being spread, with only the signal power in the vicinity of the frequency fl being lost. This effect becomes more pronounced as the period length of the pseudorandom series increases. Fig. 3(b)j(C) shows the signal spectrum according to the conventional method and an example of the demodulated spectrum demodulated through the transmission line of Fig. 3(a), and Fig. 3(d)l(e) shows the signal spectrum according to the method of the present invention. Signal Spectrum An example of a demodulated signal spectrum demodulated through the transmission path shown in FIG. 3 (,) is shown. The dotted line in FIG. 3(c) p(e)K is an example of the transmission information signal spectrum. Furthermore, the transmission characteristics of the power line vary greatly over time as the load condition changes. That is, the position of the transmission zero point changes over time. Under such circumstances, according to the conventional method, the received signal power fluctuates greatly over time, and the received signal power sharply decreases at a time when a zero point exists near the center frequency. ), it is clear that stable communication will be impossible. On the other hand, in the spread spectrum power line communication system of the present invention, even if the transmission characteristics, particularly the transmission zero point, changes over time, the received signal power hardly changes, making stable communication possible.

Furthermore, in the method of the present invention, power line noise is whitened in the demodulation process, so communication that is especially resistant to frequency-selective noise becomes possible.

Further, according to the present invention, the low frequency components and high frequency components that are attenuated during transmission become a small part of the entire spectrum, and power loss can be minimized.

(Effects of the Invention) As described above, in the conventional method, the low frequency region of the transmission path cannot be used, so it is susceptible to low-frequency cutoff distortion, and the signal power loss is large. By reducing the low frequency component of the signal and matching it with the characteristics of the transmission path, it is less susceptible to low-frequency cut-off distortion, and the signal power loss can be reduced, allowing good communication, which has great effects.

(Example) Hereinafter, an explanation will be given with reference to an example for realizing the present invention.

Figure p. 44 is a diagram showing the power line communication system of the present invention. In the figure, 400 indicates electric power, and 401 (1) ν
401(2) indicates a modem. 402(1)-402
(N) and 403(1) to 403(N) indicate terminals. 401(1) = 401 (21 modems are 4
It is passively connected to the 00 power line and performs frequency spread modulation and demodulation for communication between the terminals. In this system embodiment, only 1 m of the modem is shown for simplicity, but it is also possible to accommodate a plurality of modems in one system.

FIG. 1 is a block diagram showing an example of a modulator/demodulator that implements the system of the present invention. Reference numeral 100 is a coupler for coupling a power line and a modem, and a signal line 150 is connected to the power line via an outlet.

The coupler 100 separates the low frequency commercial power signal and the W6 frequency data signal, and the low frequency commercial power signal is connected to the signal line 15.
3 to the 1α source of the electrical equipment. First, the operation on the demodulation side will be explained. The high frequency data signal separated by the coupler 100 is outputted to the signal line 151, passes through the amplifier 101, and then inputted to the automatic gain control amplifier 103. The automatic gain control amplifier 103 has a dynamic range sufficient to compensate for fluctuations in the base product of the power line, and a signal having constant power is output to the signal line 155. Synchronous signal extraction circuit 104 from the signal on signal line 155
The clock component and frame signal of the pseudo-random signal for demodulation are extracted and output to the signal line 156. The clock signal and frame signal from the signal @156 and the initial phase signal of the modulated pseudo-random sequence on the transmitting side from the signal @iss are input to the demodulation pseudo-random sequence generator 105, and the modulated pseudo-random sequence generator is input to the signal line 157. The same pseudo-random sequence as the sequence is output. Manchester encoder 1
At 13, the demodulation pseudorandom sequence from the signal line 157 and the clock signal from 156 are subjected to an exclusive OR operation, and a Manchester encoded pseudorandom sequence is output to the signal line 169.

The signal on the signal line 169 and the input signal from the signal line 155 are
A multiplier 106 performs the multiplication and outputs the result to a signal line 159. The data signal component of the signal on the signal line 159 is extracted by a low-pass filter 507, and after being outputted to the signal line 160, it is separated into signals sent to each terminal by the demultiplexing circuit 108.

Next, the operation on the modulation side will be explained. Signals 166(1) to 166(N) from the terminal side are multiplexed by multiplexing circuit 111 and output to signal line 161. The pseudo-random sequence generator 109 generates a pseudo-random sequence using the initial phase signal corresponding to the address of the other modem modulator input from the signal line 162 and the clock input from 570, and outputs it to the signal line 163. signal! 'J! The signal 163 is sent to the signal line 17 by the Manchester encoder 114.
An exclusive OR operation is performed with the 0 clock and a Manchester-encoded pseudorandom sequence is output to the signal line 171. The Manchester encoded pseudorandom sequence for modulation on the signal line 171 and the data signal on the signal line 161 are as follows:
Multiply product modulation is performed by the multiplier 110 and the signal line 164
is output to. In the adder 112, the sum of the modulation signal from the signal line 164 and the synchronization signal from the signal line 168 is calculated, and after outputting it to the signal line 167, it is sufficiently amplified by the amplifier 102. After attenuating low frequency components so that they do not overlap with the frequency of the signal, the signal is transmitted to the power line.

As described above, spread spectrum power line communication becomes possible. In this power line transport system, the initial phase of the Manchester-encoded pseudo-random sequence during modulation can take multiple types, so multiple types of modulators can be selected, and multi-access systems can also be configured in an expanded manner. . In addition, in spread spectrum modulation, the modulation spectrum is spread over a wide band, so the spectrum density is low), and the negative impact on other devices is significantly reduced.

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[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining one embodiment of the present invention, FIGS. 2(a) to (c) are diagrams showing frequency spectra of signals in the spread spectrum modulation process, and FIGS. 3(a) to (e) ) is a diagram showing an example of power line transmission characteristics and the signal spectrum of this method and the conventional method. Figure 4 is a diagram showing an example of a system configuration using this method. Figure 5 (a) to (+() are spread spectrum diagrams. It is a diagram showing the timing of the modulation process in the communication system. In the diagram, 400...power line, 401(1) p401(2)...
・Henjinchoki, 402 (11-402 (N), 403 (1
1 to 403 (N)...Terminal, 100...Coupler,
101, 102... Amplifier, 103... Automatic gain control amplifier, 104... Synchronization extraction circuit, 105ν109
...pseudo random sequence generator, 106r110...
Multiplier, 112...Adder, 1131114...Manchester encoder, 107...Low pass filter, 108...Muxing/demultiplexing circuit, 111...Multiplexing circuit Show 2 diagram-Ω i Figure 4 Figure 5

Claims (1)

[Claims] On the transmitting side, the information signal is spread spectrum modulated using a phase-encoded pseudo-random sequence, and after attenuating low frequency components with a filter in the coupler, it is sent to the power line, and on the receiving side. The input signal from the power line is separated into commercial power and a high frequency spread spectrum signal by a filter in a coupler, and the separated high frequency spread spectrum signal is despread spectrum demodulated using a pseudorandom sequence encoded with the same phase as that on the transmitting side. A spread spectrum power line communication method characterized by obtaining information signals and performing communication.