JP5709169B2 - Spread spectrum communication system - Google Patents

Description

  The present invention relates to a communication system and communication apparatus for AC power line communication (PLC) for transmitting transmission data having a frame structure by performing spread spectrum modulation.

When planning power saving measures, it is indispensable to know when and where how much power is being used, so the spread of power visualization systems for each office and factory has begun.
In order to make a more detailed power saving plan, it is necessary to visualize the power in each unit of distribution board in the office and further in each unit of breaker, but since the number of required power measuring machines increases, That cost is a problem.
Therefore, there is a need for a power visualization system that does not increase prices or increase installation costs.

In a conventional power visualization system, power information such as power consumption is wired or wireless.
In the case of wired communication using a LAN, if the number of measuring devices increases, the wiring becomes complicated and the cost for wiring increases, so the versatility is low.
When wireless communication such as WiFi (registered trademark) or Zigbee (registered trademark) is used, the cost of the wireless communication device is increased, and low power consumption of wireless communication becomes a problem.

Since the power visualization system requires a large number of power measuring instruments, the cost is a problem.
If a low frequency PLC is used, a system can be constructed at low cost without newly laying a communication cable.
However, since the AC power line is noisy, there is a risk that communication will be abnormal and communication will not be possible.

In general, in a poor transmission environment, a spread spectrum communication method and an error correction code with a large number of redundant bits are employed.
Transmission data is assembled into a frame and transmitted, and retransmission control (ARQ: Automatic Repeat reQuest) is performed on a frame basis.
Error detection and error correction are often performed on a frame basis.
Therefore, frame synchronization is executed by inserting a frame synchronization signal at the beginning of the frame or by distributing the frame synchronization signal in transmission data within the frame and transmitting the frame synchronization (see Patent Document 1, however, this technique is Does not use spread spectrum communication).
However, when the frame length is short, the transmission efficiency decreases if a frame synchronization signal is inserted into the transmission data.
For example, when a 16-32-bit frame synchronization signal is inserted into a 64-bit frame, there is a problem that transmission efficiency is significantly reduced.

Japanese Patent No. 3511520

"Spread spectrum communication", Yukiji Yamauchi, Tokyo Denki University Press, 1994

The present invention has been made in order to solve the above-described problems, and enables stable communication that is not easily affected by noise, and has a frame configuration on the reception side without inserting a frame synchronization signal on the transmission side. It is an object of the present invention to provide an AC power line spread spectrum communication system.
In addition, although the present inventors previously invented the spread spectrum communication system and applied for a patent (Japanese Patent Application No. 2010-134937), the present invention relates to an AC power line.

(1) The present invention is an AC power line spread spectrum communication system in which transmission data having a frame structure is subjected to spread spectrum modulation to be converted into a code string, and a signal generated by OFDM modulation for each code is transmitted.
The data to be transmitted is composed of an error correction code in addition to information indicating the amount of power.
In data transmission, first, spread modulation is performed on transmission data.
In spread modulation, a plurality of spread codes are used by switching every frame.
Next, OFDM modulation is performed on each code of the spread code string that is spread-modulated data.
A subcarrier is assigned to each piece of information constituting a code using inverse Fourier transform, and a transmission signal is generated by combining all subcarriers, and is superimposed on the power line.
The frequency of the subcarrier to be used is determined so as not to use a frequency that is an integral multiple of the frequency of the AC power or a frequency that is susceptible to noise.
In data reception, first, OFDM demodulation is performed on the received signal.
Fourier transform is performed to extract information indicated by each subcarrier.
Next, spread demodulation is performed on the OFDM demodulated data.
In spread demodulation, spread demodulation is performed using a plurality of reference codes corresponding to a plurality of spread codes used at the time of spread modulation, and frame data is identified and received data is obtained by performing spread demodulation by switching the reference codes.
Since the transmission data is transmitted after being subjected to spread spectrum modulation, it is less susceptible to noise and enables stable communication.
Furthermore, by performing OFDM modulation, it is possible to improve resistance to interference and noise and to improve transmission speed.
By switching and using spreading codes for each frame on the transmission side, the frame configuration can be identified on the reception side.
Therefore, the frame structure can be identified on the receiving side without inserting a frame synchronization signal into the transmission data on the transmitting side.

(2) In the AC power line spread spectrum communication system communication system according to the present invention, first and second spreading codes are respectively assigned as a plurality of spreading codes, and frame-structured transmission data is referred to as first and second spreading codes. OFDM that uses subcarriers that do not use a frequency that is an integral multiple of the frequency of AC power or a frequency that is susceptible to noise for spread-modulated data by alternately switching and using for each frame Modulation is performed, and the first and second reference codes corresponding to the first and second spreading codes are used, and the frame structure is identified by alternately switching the reference codes and performing spread demodulation.
Therefore, the frame structure can be identified on the receiving side only by assigning a small number of spreading codes to the transmitting side.

In the spread spectrum communication system communication system according to the present invention, the transmission line is an AC power line and is supplied with AC power.
A transmission signal generated by OFDM modulation of spread-modulated data is transmitted as a slight change in the voltage value of the transmission line superimposed on AC power, and the spread-modulated data received via the transmission line is OFDM The signal generated by modulation is received as a slight change in the voltage value of the transmission line.

(3) The present invention is an AC power line spread spectrum receiver used in the above-described AC power line spread spectrum communication system, and is generated by synthesizing all the subcarriers assigned to the respective codes of the spread modulation code sequence. OFDM signal demodulating means, reference code generating means for generating a plurality of reference codes corresponding to the plurality of spreading codes at the same code phase, and a plurality of reference codes generated by the reference code generating means, respectively. A plurality of systems of spread spectrum demodulation means for spreading and demodulating a spread modulated signal received via the transmission line, and a sub demodulator in the OFDM demodulation means based on the demodulated signals demodulated by the plurality of systems of spread spectrum demodulation means Synchronization detecting means for detecting carrier synchronization; and in the synchronization detecting means, the spread modulated received signal and the plurality of reference codes Frame synchronization detection for acquiring the frame synchronization signal based on a timing at which any one of the signals corresponds to a state in which the spread modulated signal and the other one of the plurality of reference codes correspond to each other It has a means.
Therefore, the AC power line spread spectrum receiver used in the AC power line spread spectrum communication system can be realized with a simple configuration.

(4) The present invention is an AC power line spread spectrum communication system according to (1) or (2), which is used in a communication system that performs code division multiple access between a plurality of transmission apparatuses and one reception apparatus. The plurality of spreading codes are assigned to each of the plurality of transmitting devices so as to be different for each of the transmitting devices, and the one receiving device has all the spreading codes assigned to the plurality of transmitting devices. A plurality of spread demodulation systems each using a reference code corresponding to a code, and identifying a reference code used in a spread demodulation system in which the spread modulated signal and the reference code are associated with each other The transmission device that transmits the data obtained by selecting the output of the spread demodulation system is specified.
Accordingly, a common transmission path can be used by a plurality of transmission apparatuses and one reception apparatus.

(5) The present invention provides the AC power line spread spectrum communication system according to (4), wherein each of the plurality of transmission devices uses the power amount data of the device as transmission data of the frame configuration for a plurality of devices, respectively. Transmitting to one receiving device, the device has unique data for specifying the device, and a plurality of spreading codes assigned to each transmitting device are power amount data transmitted by the transmitting device. In association with the specific data for specifying the device that has obtained the signal, it is assigned in advance to each of the transmission devices, and the one reception device has a correspondence between the spread-modulated signal and the reference code. By identifying the reference code used in the spread demodulation system, the energy data corresponding to the data obtained by selecting the output of the spread demodulation system was obtained. The device is specified.
Therefore, in each transmitting apparatus, even if it is not necessary to insert and transmit unique data for identifying a device that obtains power amount data to the transmission data, the power amount data corresponding to the received data is received by one receiving apparatus. The obtained device can be specified.

According to the present invention described above, there is an effect that transmission data having a frame configuration can be transmitted stably and efficiently without being affected by noise.
As a result, a communication abnormality caused by noise can be prevented, and a highly reliable AC power line spread spectrum communication system that efficiently superimposes signals on an AC power line and communicates without providing a new wiring for communication is realized. .

It is a system block diagram which shows the specific example of the alternating current power line spread spectrum communication system of this invention. It is a block block diagram which shows one Example of the communication subunit | mobile_unit shown in FIG. It is a circuit diagram which shows the specific example of the driver in the communication subunit | mobile_unit shown in FIG. FIG. 4 is a block configuration diagram of a communication slave unit and a communication master unit showing an embodiment of the present invention. It is explanatory drawing which shows the outline | summary of the spread modulation process in the block block diagram in the communication subunit | mobile_unit shown in FIG. FIG. 5 is an explanatory diagram showing an outline of a spread demodulation process in the block configuration diagram in the communication master shown in FIG. 4. It is explanatory drawing which shows the data conversion procedure on the transmission side in the block block diagram of the communication subunit | mobile_unit and communication parent | base station shown in FIG. It is explanatory drawing which shows the outline | summary of the OFDM modulation in the block block diagram of the communication subunit | mobile_unit shown in FIG. It is a figure which shows the result of the computer simulation of the communication performance using each 1 unit | set of a communication subunit | mobile_unit and a communication main | base station.

Embodiments of the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a system configuration diagram showing a specific example of an AC power line spread spectrum communication system of the present invention.
One or a plurality of data on the power consumption measured using one power sensor 4a for each load 6a such as one or a plurality of electronic devices is provided between the power plug 1a and the power socket 1d of the electronic device. 1 is transmitted by a communication handset 5a (transmission device) provided for each load, and power usage data for one or a plurality of electronic device loads is transmitted superimposed on the AC power line 2 and connected to this AC power line 1 The communication data is received by one communication master device 3 (receiving device).

In this embodiment, each load connected to the AC power line 2 is provided with a power sensor 4a and communication slaves 5a to 5c.
Each power sensor monitors the power usage status of the corresponding load.
The communication slave unit 5a is a transmission device that transmits a value indicating the power detected by the power sensor 4a provided in the corresponding load 6a to the communication master unit 3 using the AC power line 2 as a transmission path.
Accordingly, each of the communication slave units 5a to 5c can also be called a measurement communication circuit.

In the embodiment of the present invention, as a transmission method, a direct spread spectrum modulation method (hereinafter simply referred to as “spread modulation”) and an orthogonal frequency division multiplexing method (hereinafter simply referred to as “spread modulation”) are used. "OFDM") is adopted, and code division multiple access (CDMA: also called code division multiple access) is adopted as a multiplexed communication system. Hereinafter, description will be made with reference to FIGS. 4, 5 a to 5 d, 2, and 3.
FIG. 4 is a block configuration diagram of the communication slave unit 5a and the communication master unit 3 showing an embodiment of the present invention.
In this block diagram, transmission data in a frame configuration is spread spectrum modulated between one communication slave unit and one communication base unit using the AC power line 2 as a transmission path, and the obtained data is subjected to OFDM modulation. A communication system using a spread spectrum communication system and an OFDM system having a one-to-one configuration for transmitting a generated transmission signal is shown.

The communication slave unit 5a (transmission device) includes a spread modulation unit 41, a spread code generator 42, and an OFDM modulation unit 48.
In one communication slave, a plurality of spreading codes, in the example shown, two spreading codes SCai and SCbi (i = 1) are assigned in advance.
Here, i is an integer value corresponding to the communication slave units 5a to 5c, and a plurality of spread codes SCai and SCbi are individually assigned to the plurality of communication slave units 5a to 5c.
The spread codes SCai and SCbi (1 to n (n is a natural number)) are all different.
In the communication slave unit 5a, the spread code generator 42 switches the spread codes SCai and SCbi for each frame and outputs them to the spread modulation unit 41.
The spread modulation unit 41 uses the spread code SCai or SCbi output from the spread code generator 42 to spread-modulate the frame-structured transmission data, and outputs the spread-modulated data to the OFDM modulation unit 48.
The OFDM modulation unit 48 performs OFDM modulation on the data output from the spread modulation unit 41 and transmits the OFDM-modulated signal to the AC power line 2 (transmission path).

In the communication master unit 3 (receiving device), the OFDM demodulator 49 demodulates the received data by OFDM, and the reference code generation unit 44 has a plurality of references corresponding to a plurality of spreading codes SCai and SCbi assigned to the communication slave unit. The codes SCai and SCbi (same as the spreading code) are generated with the same code phase.
In communication base unit 3, a plurality of spread demodulation systems that use a plurality of reference codes SCai and SCbi, respectively, have an a sequence and a b sequence in the illustrated example.
The a-sequence reference code SCai is supplied to the a-sequence spread demodulator 49, and the b-sequence reference code SCbi is supplied to the b-sequence spread demodulator 49.

The OFDM demodulator 49 performs OFDM demodulation on the OFDM-modulated signal received via the AC power line 2, and outputs the OFDM-demodulated data to the spread demodulation units 43a and 43b.
The a-sequence spread demodulation unit 43a and the b-sequence spread demodulation unit 43b use the reference codes SCai and SCbi supplied from the reference code generation unit 44 for the OFDM demodulated data output from the OFDM demodulation unit. After despreading, the spread demodulated data of system a and system b (the value after the level determination of the cumulative addition value of the product-sum operation) is output to the selection unit.
In the process of the spread demodulation process, the synchronization detection unit 45, based on the demodulated signal (correlation output value before level determination) demodulated by the spread demodulation unit, the above-mentioned spread modulated signal and a plurality of reference codes SCai , SCbi, and the phase of the OFDM fundamental frequency is controlled so that the correlation output value of the spread demodulated signal is maximized.
In the phase control, the phase of the OFDM fundamental frequency is switched in increments of the frequency of the power line frequency.

The frame synchronization detection unit 46 outputs a frame synchronization signal based on the correspondence between the spreading code and the reference code in the synchronization detection unit 45.
That is, from the state in which the spread-modulated received signal corresponds to one of a plurality of reference codes SCai and SCbi (for example, SCai) among the a-system spread demodulation unit 43a and the b-system spread demodulation unit 43b. The frame synchronization signal for identifying the frame configuration is output based on the timing at which the received signal subjected to the spread modulation and the other one of the plurality of reference codes SCai and SCbi (for example, SCbi) switch to a corresponding state.

In other words, the timing at which the spread demodulation system that corresponds to the reference code used switches from one spread demodulation system to another spread demodulation system (a system → b system, b system → a system) A frame synchronization signal is output based on
Since each bit of the reference code is associated with each subcarrier of OFDM in a predetermined manner, even if the spread demodulation system is switched, the code phase synchronization does not shift.

Each time the frame synchronization signal is output, the selection unit 47 selects the spread demodulated data output by the a-system spread demodulation unit 43a and the b-system spread demodulation unit 43b to which the spread code corresponds. The reception data corresponding to the transmission data of the communication slave unit 5a is output.
Note that the selection unit 47 can identify the spread demodulation system with which the correspondence is obtained by acquiring information on the timing of switching from the a system to the b system or the reverse timing from the frame synchronization detection unit 46.
The frame synchronization signal is used to identify the frame structure of the received data output from the selector 47 in the subsequent processing unit, extract a redundant code, perform error detection correction, and separate it into a plurality of measurement data. The

FIG. 5c is an explanatory diagram showing a data conversion procedure in the block configuration diagram of the communication slave and the communication master shown in FIG.
FIG. 5c (j) shows a procedure for generating a transmission signal by OFDM-modulating data obtained by spread-modulating transmission data in the communication slave unit 5a of FIG. 4, focusing on 1 bit of transmission data of FIG. 5a (b). .
Transmission data is first spread-modulated using the spreading code SCai or spreading code SCbi.
That is, 1-bit transmission data is replaced with a spreading code of 1023 chips.
Then, the spread-modulated data is input to the OFDM modulation unit 48 of FIG. 4, and the transmission signal generated by OFDM modulation is superimposed on the AC power line 2 to transmit the data.
The OFDM modulation section 48 divides and assigns a signal subjected to spread modulation by inverse Fourier transform to a plurality of subcarriers, and adds them to generate a transmission signal.

FIG. 5a is an explanatory diagram showing an overview of the spread modulation process in the block configuration diagram of the communication slave device 5a shown in FIG.
FIG. 5 a (a) is a frame synchronization signal in the communication slave unit 3. Reference numeral 51 indicates the generation timing of the frame synchronization signal.
The horizontal axis represents the passage of time.
FIG. 5a (b) is a bit stream of transmission data in the communication slave unit.
The example shown in the figure has a frame structure in which one frame is 75 bits.
As an example, the transmission rate (bit rate) of transmission data is 12 bps.
In the spread modulation unit 41 of FIG. 4, as shown in FIG. 5a (c), the spread code SCai and the spread code SCbi are set for each frame corresponding to the data frame to be transmitted (transmission data having a frame configuration). Switch alternately and perform spread modulation.
FIG. 5a (c) shows spreading codes SCai and SCbi (i = 1) output from the spreading code generator 42. FIG.
In both cases, the code length (length of one cycle) is 1023.
In the figure, “a” represents the spreading code SCai, and “b” represents the spreading code SCbi.
The spreading codes SCai, “1111... 110” and SCbi “10101... 111” shown in the figure are described for explanation and are not actual.
One period of the spread codes SCai and SCbi in FIG. 5a (c) corresponds to one bit period of the transmission data in FIG. 5a (b).
This 1-bit period is equal to the period of the fundamental frequency of OFDM.
Also, since the OFDM fundamental frequency is low, no OFDM transmission guard interval is provided.

The spread modulation unit 41 outputs the spread code SCai as it is when the transmission data in FIG. 5a (b) is “1”, and inverts and outputs the spread code SCai when the transmission data is “0”.
When a 75-bit series of transmission data is output in this way, the next frame is switched, so that the spread code generator 42 switches the spread code to SCbi.
The spread modulation unit 41 outputs the spread code SCbi as it is when the transmission data is “1”, and inverts and outputs the spread code SCbi when the transmission data is “0”.
When a 75-bit series of transmission data is output in this way, the next frame is switched, so that the spread code generator 42 switches the spread code to SCai.

FIG. 5d is an explanatory view showing an outline of OFDM modulation in the block diagram of the communication slave shown in FIG.
The frequency for subcarrier in FIG. 5d represents the frequency of each subcarrier allocated by dividing the signal in OFDM modulation, and the data subjected to spread modulation is the spreading code of (j) in FIG. 5c.
The fundamental frequency of the OFDM subcarrier is 1/8 of the frequency of the AC power line.
When the frequency of the AC power line is 50 Hz, the fundamental frequency of the OFDM subcarrier is 6.25 Hz.
That is, 8 times the period of the AC power line is the period of the fundamental frequency of OFDM.
If the point at which the AC power line voltage shifts from minus to plus (zero cross point) is used as the phase reference for the OFDM fundamental frequency, OFDM demodulation signal processing can also be performed by using this zero cross point as the phase reference when demodulating OFDM. Easy to do.
The subcarrier frequency is determined so as not to use a frequency that is an integral multiple of the frequency of the AC power or a frequency that is susceptible to noise from the AC power.
For example, the basic frequency of the subcarrier is set to 6.25 Hz, and the frequency of each subcarrier is determined so as not to use a frequency of 500 Hz or more and an integer multiple of 50 Hz.
1023 subcarriers are used so that one subcarrier is assigned to one chip of the spread code.
Therefore, in the example of FIG. 5d, the maximum frequency of the subcarrier is 7086.25 Hz.
The waveform of the subcarrier in FIG. 5d schematically shows a waveform corresponding to each subcarrier.
The waveform to be used is determined based on the spread modulated data.
When one chip of spread-modulated data is “1”, the waveform indicated by the corresponding subcarrier is used as it is.
When one chip of spread-modulated data is “0”, the waveform indicated by the corresponding subcarrier is not used, and is handled as an empty state.
A transmission signal is generated by adding all the 1023 waveforms to be used determined in this way.
The transmission data subjected to spread modulation generates transmission signals by turning on / off the subcarriers as shown in FIG. 5 in correspondence with the spread modulated “1” and “0” outputs, and superimposes them on the transmission path.
On / off of the subcarrier is OOK (on / off keying).
An OFDM-modulated waveform can be calculated in advance, stored in a data memory, and read out for use.
The OFDM-modulated transmission waveform is uniquely determined corresponding to the combination of the used spreading codes SCai and SCbi and the transmission data “0” and “1”.
Therefore, by storing the transmission waveform calculation results corresponding to all spreading codes in the data memory in advance, refer to the data memory that stores the transmission waveform without performing OFDM modulation digital signal processing operation. A transmission waveform can be obtained simply by doing.
In this way, it is possible to calculate the transmission waveform in advance and refer to the data memory. In this case, the signal processing circuit can be simplified and the power consumption in the slave unit can be reduced.

FIG. 5c (k) shows a procedure for extracting the received data by performing OFDM demodulation after the signal received by communication base unit 3 in FIG. 4 and corresponding to 1 bit of the received data in FIG. 5a (i). .
First, the received signal is input to the OFDM demodulator 49 shown in FIG.
The OFDM demodulator 49 extracts data indicated by each subcarrier from the added signal by Fourier transform.
The extracted data is data 1023 that is the same as the code length of the spreading code before OFDM modulation in FIG. 5c (j).
Next, the OFDM demodulated signal is spread and demodulated in the spread demodulation section 49 of FIG.
The spread demodulated data becomes reception data corresponding to transmission data.
Regarding the phase synchronization, since the period of the fundamental frequency of OFDM is 8 times the period of the AC power line, the OFDM signal can be easily synchronized by performing an FFT operation on the received signal using the zero cross point of the AC power line as a phase reference. Can be supplemented.
In addition, once synchronization of OFDM subcarriers is established, timing information can be obtained continuously through the AC power line, so synchronization tracking is very easy based on the frequency of the AC power line.
The OFDM demodulator 49 demodulates each subcarrier signal by Fourier transform.
For subcarriers with high frequency, even if there is a slight timing shift, the phase changes greatly, but because on-off keying modulation is performed, there is no information on the phase of each demodulated subcarrier, and each subcarrier Corresponds to the data indicated by each subcarrier.
The OFDM demodulator 49 outputs the amplitude of each subcarrier after Fourier transform.

FIG. 5b is an explanatory diagram showing an overview of the spread demodulation process in the block configuration diagram of the communication parent device 3 shown in FIG.
The OFDM demodulated signals (amplitude values of the subcarriers) received by the communication master unit of FIG. 4 are respectively referred to as reference codes SCai in the a system spreading demodulation unit 43a and the b system spreading demodulation unit 43b. Multiply by each chip with SCbi, and spread and demodulate by accumulatively adding all bits (1023 chips) of the reference code.
The synchronization detection in the synchronization detection unit 45 is realized by searching for the phase of the OFDM fundamental frequency (start timing of the fundamental period) that maximizes the absolute value of the cumulative addition value of the product-sum operation.
FIG. 5 b (d) and FIG. 5 b (e) are spread demodulated data of each system, and are output to the selection unit 47.
The spread demodulated data is acquired by determining the magnitude of the cumulative addition value at the timing when the absolute value of the cumulative addition value of the product-sum operation described above is maximized.
Here, the symbol “−” indicates that the level determination could not be performed for either the data bit “0” or “1” because the cumulative addition value did not exceed the predetermined threshold as a result of the determination of magnitude. ing.
As for the level determination method, the order of magnitude of the amplitude of each subcarrier may be used instead of the amplitude of each subcarrier.
That is, in descending order of the magnitude of the amplitude of the demodulation result of each subcarrier,
For half the number of spreading codes, the subcarrier amplitude is set to “1” and the remaining subcarrier amplitude is set to “0” to calculate the cumulative added value.
In this case, even when there is a subcarrier whose amplitude is excessive due to the influence of noise or the like, the influence of the noise can be suppressed, and a more reliable level determination can be performed.
Thereby, noise tolerance of communication quality can be improved.

FIG. 5B (f) shows a code detection signal output when a corresponding code is detected in the spread demodulation unit 43a.
Reference numeral 52 indicates the generation timing of the code detection signal.
FIG. 5B (g) shows a code detection signal output when a corresponding code is detected in the spread demodulation unit 43b.
Reference numeral 53 indicates the generation timing of the code detection signal.
5b (d) and FIG. 5b (f) correspond to each other, and “0” or “1” is output at the generation timing of the phase synchronization signal. FIG. 5 b (e) and FIG. 5 b (g) correspond similarly.

The frame synchronization detection unit 46 in FIG. 4 detects the timing (frame boundary timing) at which the system outputting the phase synchronization signal shown in FIGS. 5b (f) and 5b (g) is changed, and FIG. ) Is output.
Reference numeral 54 denotes the generation timing of the frame synchronization signal.
The selection unit 47 in FIG. 4 receives the instruction of the spread demodulation system to which the correspondence is taken from the frame synchronization detection unit, and the demodulation of the spread demodulation unit 43a shown in FIG. The data or the demodulated data of the spread demodulation unit 43b shown in FIG. 5b (e) is alternatively selected, and the received data shown in FIG. 5b (i) is output.

The reception process in the communication parent device 3 described above is an example, and various methods can be employed for the synchronization detection method and the selection of the system that is compatible.
For example, the demodulation result of the spread demodulation unit 43a (cumulative addition value of the product-sum operation before level determination) is R_SCai, and the demodulation result of the spread demodulation unit 43b is R_SCbi. At this time, with respect to the absolute value of R_SCai and the absolute value of R_SCbi, the larger absolute value is the received data in code phase synchronization, and the magnitude of the demodulation result corresponds to “1” and “0” of the received data, respectively.
The system from which received data is obtained is switched from one of R_SCai and R_SCbi to the other, thereby determining frame switching.
Thereby, frame synchronization in the reception process can be easily established.

In the above description, two spread codes SCai and SCbi are assigned to one communication slave unit 5a.
However, another spread code SCci may be assigned to one communication slave unit 5a. Instead of transmitting normal monitoring data, another spreading code SCci may be used for a frame when transmitting control interruption data or the like from the communication slave unit 5a to the communication master unit 3. .
In this case, the communication master unit 3 simultaneously processes three spread demodulation systems using the reference codes SCai, SCbi, and SCci corresponding to the spread codes assigned to one communication slave unit 5a.

Further, when transmitting normal monitoring data, a plurality of spread codes of 3 or more may be assigned.
For example, the spread codes SCai, SCbi, and SCci are switched in units of frames and transmitted.
In the communication base unit 3, in the spread demodulation system using the reference codes SCai, SCbi, and SCci, the frame synchronization can be detected by switching the spread demodulation system that can synchronize the code phase, that is, the reference code that can be synchronized.

The description with reference to FIG. 4, FIG. 5 a to FIG. 5 d is for an AC power line spread spectrum modulation communication system in which one communication slave unit 5 a is a transmission device and one communication master unit 3 is a reception device.
On the other hand, the indoor AC power line wiring system illustrated in FIG. 1 is an AC power line spread spectrum modulation communication system in which a plurality of communication slave units 5a to 5c are used as transmitting devices and one communication master unit 3 is used as a receiving device. .
Each of the communication slave units 5a to 5c superimposes the independently spread modulated signals on the AC power line 2 asynchronously with each other.

In the case of FIG. 1, the communication master unit 3 needs to separate and receive the spread modulated signals transmitted from the plurality of communication slave units 5 a to 5 c.
For this purpose, in the embodiment shown in FIG. 1, a different spreading code is assigned to each of a plurality of communication slave units.
Scai and Scbi (i = 1 to 3) are assigned to the communication slave units 5a to 5c, respectively.
Therefore, a total of (2 × i) types of spreading codes different from each other are used.
The communication master unit 3 uses a total of (2 × i) types of reference codes Scai, Scbi (i = 1 to 3) at the same time, and transmits the reference codes Scai, Scbi (i = 1 to 3) is used to perform spread demodulation of the a system and the b system to obtain received data. A transmission that transmits data obtained by selecting the output of the spread demodulation system by identifying the type of the reference code used in the spread demodulation system in which the spread modulated signal and the reference code correspond to each other The device, that is, the communication slave unit of the transmission source is specified.
Different spreading codes Scai and Scbi (i = 1 to 3) can be arbitrarily assigned to the communication slave unit.

FIG. 3 is a circuit diagram showing a specific example of a driver circuit for outputting a transmission signal in the communication slave unit 5a shown in FIG.
In FIG. 3, the output of the driver circuit is connected between AC power lines 2a and 2b.
The driver circuit receives the waveform data of the OFDM-modulated transmission signal output from the CPU 16 shown in FIG. 2, and sets the time ratio of the PWM modulation circuit 31 so that the waveform indicated by the waveform data is output.
The FET is turned on / off by the output of the PWM modulation circuit and smoothed by the inductor L1 and the capacitor C1 to generate a transmission signal.
This transmission signal is connected to the AC power line via the capacitor C2.

Furthermore, in the driver of FIG. 3, it is possible to obtain a power source necessary for the operation of the communication slave unit 5a.
That is, in the driver of FIG. 3, power is obtained from the AC power line by superimposing an AC component of 50 Hz to 60 Hz synchronized with the power supply frequency on the transmission signal waveform in the same phase as the AC power line.
Thereby, a part of the power supply circuit that has been separately provided in the past can be omitted, and the number of parts of the circuit of the communication slave unit 5a can be reduced.

FIG. 6 is a diagram showing a result of computer simulation of communication performance using one each of the communication slave unit and the communication master unit with respect to the effect in the implementation of the present invention.
In the figure, the vertical axis represents the bit error rate (BER), and the horizontal axis represents the signal-to-noise ratio (SNR) in dB.
The solid line in the figure represents an example of the present invention when communication is performed assuming a communication path with each signal-to-noise ratio in an environment in which one communication slave unit and one communication master unit are connected by an AC power line. Represents the bit error rate after communication.
This simulation result shows that the bit error rate is sufficiently small and communication is possible even when the SNR is −13 dB, that is, the noise is about 20 times larger than the signal.

The AC power line spread spectrum communication system shown in FIG. 1 transmits power usage data obtained by measuring loads 6a to 6c such as electronic devices to the receiving device side.
Accordingly, the measurement object is loads 6a to 6c such as electronic devices.
Manufacturers' serial numbers such as SN001 to SN003 described in FIG. 1 are assigned to the loads 6a to 6c such as electronic devices.
Accordingly, spreading codes Scai and Scbi (i = 1 to 3) individually assigned to each of the communication slave units 5a to 5c have loads 6a to 6c for obtaining measurement data transmitted by each of the communication slave units 5a to 5c. In association with specific data to be identified, for example, a manufacturer's serial number, it is assigned in advance to the plurality of communication slave units 5a to 5c.
Data obtained by selecting the output of the spread demodulation system by identifying the reference code used in the spread demodulation system in which the correspondence between the spread modulated signal and the reference code is taken. The loads 6a to 6c that have obtained the measurement data corresponding to are specified.
In this way, it is possible to identify the loads 6a to 6c to be measured on the receiving device side without inserting the above-described manufacturing number or the like into the transmission data.

An AC power line spread spectrum communication system applied to PLC (Power Line Communication) using a commercial AC power line (including only indoor wiring) as a transmission path has been described.
When applied to smart meter communication, it is possible to monitor and collect data on the power meter and accumulated energy data of each facility distributed by the power company. The load can be controlled as necessary from the amount of power generation, and the load status can be monitored and an abnormality can be detected.

1a-1c, 1g Outlet plug 1d-1f Outlet socket 2 AC power line 2a, 2b AC power line 3 Communication master unit 4a-4c Power sensor 5a-5c Communication slave unit 6a-6c Load 11 Voltage divider 12 Current divider 13 Current amplifier 14 Signal Switcher 15 A / D converter 16 CPU
18 driver 31 PWM modulation circuit 41 spreading modulation unit 42 spreading code generator 43a a system spreading demodulating unit 43b b system spreading demodulating unit 44 reference code generating unit 45 synchronization detecting unit 46 frame synchronization detecting unit 47 selecting unit 48 OFDM modulating unit 49 OFDM Demodulator

Claims (5)

An AC power line spread spectrum communication system for transmitting a signal generated by OFDM modulation of each code of a code string obtained by performing spread spectrum modulation conversion on transmission data in a frame configuration,
A plurality of spreading codes are assigned, and the transmission data of the frame configuration is spread and modulated by switching the spreading codes for each frame,
A signal generated by combining all the subcarriers assigned to each code of the spread code sequence subjected to spread modulation is transmitted to the transmission line,
A plurality of spread demodulation systems using a plurality of reference codes corresponding to the plurality of spread codes, respectively,
The plurality of spreading demodulation systems spread and demodulate the spreading code string from subcarrier information obtained by decomposing the transmitted signal received via the transmission path,
The spread demodulation system in which the spread modulated signal and the reference code are associated with each other identifies the frame configuration based on the timing at which one spread demodulation system is switched to another spread demodulation system,
The received data is output by selecting the output of the spread spectrum demodulation system that takes the above-mentioned correspondence,
An AC power line spread spectrum communication system. A first spreading code and a second spreading code are assigned as the plurality of spreading codes;
The frame-structured transmission data is spread-modulated by alternately switching the first spreading code and the second spreading code every frame,
The subcarriers are assigned to frequencies excluding the frequency of AC power and integer multiples thereof,
As the plurality of spread demodulation systems, there are first and second spread demodulation systems,
Based on the timing at which the spread demodulation system in which the spread modulated signal and the reference code are associated with each other is alternately switched between the first spread demodulation system and the second spread demodulation system, Identifying the frame configuration;
The AC power line spread spectrum communication system according to claim 1. An AC power line spread spectrum receiver used in the AC power line spread spectrum communication system according to any one of claims 1 to 2,
OFDM demodulating means for a signal generated by synthesizing all subcarriers assigned to each code of the spread code sequence subjected to the spread modulation;
Reference code generating means for generating a plurality of reference codes corresponding to the plurality of spreading codes at the same code phase;
A plurality of spread demodulation means for spreading and demodulating a spread modulated signal received via the transmission path using a plurality of reference codes generated by the reference code generation means,
Synchronization detection means for detecting the synchronization of subcarriers in the OFDM demodulation means based on the demodulated signals demodulated in the spread demodulation means of the plurality of systems;
In the synchronization means, the spread-modulated signal and the other one of the plurality of reference codes correspond from the state in which the spread-modulated received signal corresponds to any one of the plurality of reference codes. Frame synchronization detection means for acquiring the frame synchronization signal based on the timing of switching to a state of
An AC power line spread spectrum receiving apparatus comprising: The AC power line spread spectrum communication system according to any one of claims 1 to 2, which is used in a communication system that performs code division multiple access between a plurality of transmission devices and one reception device. ,
For each of the plurality of transmission devices, the plurality of spreading codes are assigned to be different for each transmission device,
The one receiving device is:
A plurality of spreading demodulation systems each using each reference code corresponding to each spreading code assigned to the plurality of transmission devices,
A transmission that transmits data obtained by selecting an output of the spread demodulation system by identifying a reference code used in a spread demodulation system in which the spread modulated signal and the reference code are associated with each other Identify the device,
An AC power line spread spectrum communication system. Each of the plurality of transmission devices transmits the power amount data of the device as a transmission data of the frame configuration to the one reception device for a plurality of devices,
The device has unique data that identifies the device,
The plurality of spreading codes assigned to each of the transmission devices is assigned in advance to each of the transmission devices in association with unique data that identifies the device that has obtained the power data transmitted by the transmission device. And
The one receiving device is obtained by selecting an output of the spread demodulation system by identifying a reference code used in a spread demodulation system in which the spread modulated signal and the reference code are associated with each other. Identify the device that obtained the energy data corresponding to the received data,
It is characterized by
The AC power line spread spectrum communication system according to claim 4.

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