JP2012075012A - Communication system, transmitter and receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly start receiving data without the need of synchronization capture at a receiving side in a communication system that is configured to switch the communication system to either one of an OFDM system and an SS system, when the communication system is switched to the SS system.SOLUTION: A communication system comprises a transmitter 10 and a receiver 30. The transmitter 10 includes: an OFDM transmitting section 12; a DSSS synchronization signal generating section 16; and a DSSS transmitting section 14. The DSSS synchronization signal generating section 16 generates a synchronization signal that presents a diffusion frequency of the DSSS transmitting section 14 when the transmitter 10 transmits data via the OFDM transmitting section 12. The generated synchronization signal is transmitted to the receiver 30 side by using a sub-carrier of an OFDM signal. The receiver 30 side includes: an OFDM receiving section 32; a DSSS synchronization timing determination section 36; and a DSSS receiving section 34. The DSSS synchronization timing determination section 36 fetches the synchronization signal from a data processing section 42 and stores synchronization timing when the OFDM receiving section 32 receives the data. Synchronization timing after switching the communication system that is estimated from a plurality of the synchronization timings stored in the past is output to the DSSS receiving section 34 when the communication system is switched to the DSSS system.

Description

  The present invention relates to a communication system configured to be able to switch a communication method to either an orthogonal frequency division multiplexing method or a spread spectrum method, and a transmission device and a reception device suitable for constructing the communication system.

  Conventionally, in a communication system that performs data communication via a signal line such as a power line, in order to perform high-speed data communication without being affected by noise superimposed on the signal line, the communication method is orthogonal. Switching to either a frequency division multiplexing system (hereinafter also referred to as OFDM system) or a spread spectrum system (hereinafter also referred to as SS system) has been proposed (see, for example, Patent Document 1).

  According to the proposed communication system, the OFDM system capable of high-speed communication is set as the communication system under the usage conditions in which the noise around the system is reduced. Under use conditions where normal data communication cannot be performed, the communication system is switched to the SS system, which has higher noise resistance than the OFDM system.

  Therefore, according to the proposed communication system, the communication method can be set to a communication method that can obtain the maximum communication speed under the environmental conditions during communication while ensuring the communication quality of data communication.

JP 2008-301408 A

  By the way, if the communication method is switched as in the above proposal, data communication cannot be performed at the time of switching, and therefore it is necessary to shorten the time required for switching as much as possible.

  However, in the SS system, the transmission signal is spread using a spreading code, a hopping pattern, etc., so that when the receiving apparatus restores data from the received signal, the restoration operation is performed on the transmission signal on the transmitting apparatus side. It is necessary to perform synchronization acquisition in order to synchronize with the spreading period of the.

  For this reason, in the proposed communication system, when the communication method is switched from the OFDM method to the SS method, it takes time until normal data communication can be executed for synchronization acquisition on the receiving device side. There was a problem that it took.

  The present invention has been made in view of such problems, and in a communication system configured to be able to switch the communication method to either the OFDM method or the SS method, when the communication method is switched to the SS method, the receiving side An object of the present invention is to enable data reception to be started promptly without performing synchronization acquisition.

  2. The communication system according to claim 1, wherein the transmitting apparatus includes a first modulation means of orthogonal frequency division multiplexing (OFDM) and a second modulation of spread spectrum (SS). And a modulation means used for transmission of transmission data is switchable between the first modulation means and the second modulation means.

  Further, the receiving device includes a first demodulation unit of an orthogonal frequency division multiplexing (OFDM method) for restoring transmission data transmitted from the transmission device via the first modulation unit, and a second modulation unit from the transmission device via the second modulation unit. And spread spectrum system (SS system) second demodulation means for restoring transmitted data transmitted in this manner.

  For this reason, according to the communication system of the present invention, as in the above-described prior art, the communication method is changed to a communication method that can obtain the maximum communication speed under the environmental conditions during communication while ensuring the communication quality of data communication. It becomes possible to set.

  In the communication system of the present invention, on the transmission device side, the synchronization signal generation means generates a synchronization signal representing a spreading period when the second modulation means converts transmission data into a transmission signal, and the synchronization signal is Superimposed on a part of the transmission signal output from the first modulation means, on the receiving device side, the synchronization timing setting means extracts the synchronization signal from the received data restored by the first demodulation means, and the extracted Based on the synchronization signal, the second demodulation means sets a synchronization timing necessary for restoring the reception data from the reception signal.

  Therefore, according to the communication system of the present invention, when the transmission apparatus switches the modulation means used for data transmission from the first modulation means of the OFDM scheme to the second modulation means of the SS scheme, In the second demodulating means, the restoration operation of the received data can be started promptly without executing signal processing for synchronization acquisition.

  Therefore, according to the communication system of the present invention, the time required for switching the communication method from the OFDM method to the SS method can be shortened, and normal data communication can be started immediately after the communication method is switched.

  By the way, in the communication system of the present invention, since the communication method for performing data communication between the transmission device and the reception device is switched, it is necessary to synchronize the switching timing between the transmission device and the reception device.

  For this purpose, a communication system switching command may be simultaneously input to the transmission device and the reception device from a higher-level control device that monitors the communication conditions. The transmission data transmitted to the receiving device may include switching timing data indicating the timing for switching the communication method, so that the transmitting device notifies the receiving device of the switching timing of the communication method.

  In particular, in order to notify the transmission apparatus from the OFDM system to the SS system, the transmission apparatus outputs the first modulation means to the transmission apparatus as described in claim 2. Switching request generating means for superimposing the switching request signal on a part of the transmission signal to be received, and the receiving apparatus extracts the switching request signal from the received data restored by the first demodulating means and uses the second demodulating means to It is preferable to provide switching request determination means for starting data reception.

  That is, in this way, the transmission apparatus directly notifies the reception apparatus of the switching request using a part of the transmission signal output from the first modulation means (specifically, the subcarrier constituting the OFDM signal). Thus, the configuration for notifying the switching request can be simplified.

  In addition, on the receiving device side, switching from the OFDM method of the communication method to the SS method can be detected easily and quickly from the signal level of the subcarrier of the received signal (OFDM signal), and the demodulation means to be used Switching (specifically, switching from the first demodulating means to the second demodulating means) can be performed quickly without a response delay.

  Further, when the switching request signal is superimposed on a part of the transmission signal output from the first modulation means (specifically, the subcarrier constituting the OFDM signal) in this way, the subcarrier is different from the subcarrier on which the synchronization signal is superimposed. Is used, the number of subcarriers available for data transmission by the first modulation means is reduced, and the communication speed is reduced.

  Therefore, as described in claim 3, the synchronization signal generation unit superimposes the synchronization signal on a part of the subcarrier output as the transmission signal from the first modulation unit, thereby generating the synchronization signal from the first modulation unit. The switching request generation means may be configured to transmit the switching request signal by changing a change pattern (pulse width or the like) of the synchronization signal superimposed on a part of the subcarrier by the synchronization signal generation means.

  That is, in this way, the synchronization signal and the switching request signal can be transmitted using the same subcarrier, and the number of subcarriers used for transmitting each of these signals is reduced, so that the OFDM system can be used. It is possible to prevent the communication speed from being lowered.

  On the other hand, the communication system according to claim 4 includes a plurality of communication devices, and one of the communication devices serves as a master and transmits a signal to another communication device (slave side communication device). The present invention relates to a master-slave type communication system that replies to a transmission signal from a master side communication device.

  The master side communication device is provided with a master side transmission device configured similarly to the transmission device according to claim 1, and the slave side communication device is configured similarly to the reception device according to claim 1. A slave-side receiving device is provided.

  For this reason, according to the communication system according to claim 4, when data transmission is performed from the master side transmission apparatus to the slave side reception apparatus, the communication system is the OFDM system or the communication system as in the communication system according to claim 1. By switching to the SS system, the communication system used for data communication can be set to a communication system that can obtain a higher communication speed while ensuring communication quality. In addition, when the communication method is switched from the OFDM method to the SS method, the slave-side receiving device can quickly start the operation of restoring received data without performing synchronization acquisition.

  Further, in the communication system according to the fourth aspect, since it is necessary to perform data communication for return from the slave side communication device to the master side communication device, the slave side communication device includes an orthogonal frequency division multiplexing system ( (OFDM) third modulation means and spread spectrum (SS) fourth modulation means, and the modulation means used for data transmission can be switched between the third modulation means and the fourth modulation means. Slave side transmitting apparatus is provided, and the master side communication apparatus includes third demodulating means of orthogonal frequency division multiplexing (OFDM system) and fourth demodulating means of spread spectrum system (SS system). A master side receiving device is provided.

  The SS-type fourth modulation means provided in the slave side transmission apparatus is configured to convert transmission data into a transmission signal in synchronization with the synchronization timing of the second demodulation means set by the synchronization timing setting means. The fourth demodulator of the SS method provided in the master side receiver is a transmission transmitted from the slave side transmitter via the fourth modulator in synchronization with the synchronization signal generated by the synchronization signal generator. Configured to restore data.

  Therefore, according to the communication system of the fourth aspect, when data is transmitted (returned) from the slave-side transmitting device to the master-side receiving device, the communication method is switched to the OFDM method or the SS method. The communication method used for the communication method can be set to a communication method capable of obtaining a higher communication speed while ensuring communication quality.

  Further, since the fourth modulation means and the fourth demodulation means perform modulation or demodulation operation in synchronization with the second demodulation means and the second modulation means, the fourth demodulation means receives the received data without performing synchronization acquisition. The restoration operation can be started immediately.

  In the communication system according to claim 4, the master side transmission device is provided with the switching request generation means according to claim 2, and the slave side reception device is provided with the switching request determination means according to claim 2. Thus, the same effect as that of the communication system according to claim 2 can be obtained. In this case, if the synchronization signal generating means and the switching request generating means are configured as described in claim 3, the same effect as that of the communication system according to claim 3 can be obtained.

  By the way, in the present invention (claims 1 to 4), for example, when noise occurs around the system, such as a transmission path of a transmission signal from the transmission device to the reception device, the reception signal (OFDM) is generated on the reception device side due to the noise. It is conceivable that the synchronization signal cannot be extracted from the signal).

  If the synchronization signal cannot be extracted on the receiving device side and the synchronization timing of the second demodulator cannot be set by the synchronization signal, synchronization acquisition must be performed when the communication method is switched from the OFDM method to the SS method. Therefore, the effects described above cannot be obtained.

Therefore, in order to prevent such a problem, the communication system of the present invention (Claims 1 to 4) may be further configured as described in Claims 5 to 8.
That is, first, in the communication system according to the fifth aspect, the frame period of the transmission signal generated by the first modulation means is made shorter than the generation period of the noise component periodically generated around the communication system.

  This is because in OFDM communication, if noise occurs in the preamble part at the beginning of the frame, communication for each frame becomes impossible. In claim 5, the frame period is made shorter than the noise generation period. Thus, it is possible to prevent communication from being disabled due to noise generated in the preamplifier portion at the head of the frame.

  In addition, in claim 5, in order to more reliably prevent the occurrence of communication failure due to the periodically generated noise component, as described in claim 6, the first modulation means transmits the transmission signal. When generating, the frame period may be changed randomly. That is, in this way, it is possible to make it less susceptible to the influence of periodically generated noise components during communication in the OFDM scheme.

  Next, in the communication system according to claim 7, when the synchronization signal generation unit superimposes the synchronization signal on a part of the transmission signal output from the first modulation unit, the subcarriers constituting the transmission signal Among them, the synchronization signal is superimposed on a plurality of subcarriers having a frequency difference larger than the frequency band of noise components generated around the communication system.

  This is to prevent the synchronization signal from being transmitted due to the noise component generated in the frequency band including the subcarrier when the synchronization signal generating means has one subcarrier on which the synchronization signal is superimposed. In addition, even if the synchronization signal generating means has a plurality of subcarriers on which the synchronization signal is superimposed, if noise occurs in a frequency band including the plurality of subcarriers, the synchronization signal cannot be transmitted due to the noise component. It is.

  That is, in the communication system according to claim 7, the frequency band of the noise component generated around the system is measured in advance, and the synchronization signal generating means has a frequency difference larger than the frequency band of the measured noise component. By configuring the synchronization signal to be superimposed on one or more subcarriers, the synchronization signal can be transmitted more reliably from the transmission device to the reception device.

  Further, in the communication system according to claim 8, when the demodulating means used for data reception is switched from the first demodulating means to the second demodulating means on the receiving device side, the synchronization timing setting means The timing is estimated from the synchronization timing set a plurality of times in the past.

  This is because the receiver may not be able to normally receive the synchronization signal due to ambient noise, and the synchronization timing immediately after the communication method is switched from the OFDM method to the SS method is set only by the synchronization signal received last time. This is because it is considered that the synchronization timing cannot be set normally.

  That is, in the communication system according to claim 8, for the synchronization timing immediately after the demodulating means is switched from the first demodulating means to the second demodulating means, using the synchronization timing set a plurality of times in the past, for example, By estimating the synchronization timing interval to be a past average value, the synchronization timing immediately after the demodulation means is switched can be set accurately.

  The synchronization timing setting means may always set the synchronization timing according to the above procedure, not only immediately after the demodulation means is switched from the first demodulation means to the second demodulation means.

Next, the invention described in claims 9 to 14 is an invention relating to a transmission apparatus suitable for constructing the communication system of the present invention described above.
The transmission device according to claim 9 includes first orthogonal frequency division multiplexing first modulation means and spread spectrum second modulation means, wherein the modulation means used for transmission of transmission data is the first modulation. And a synchronization signal representing a spreading period when the second modulation means converts the transmission data into a transmission signal. And the synchronization signal is superimposed on a part of the transmission signal output from the first modulation means.

  Therefore, according to the transmission device according to claim 9, the transmission device functions as the transmission device in the communication system according to claim 1 or the master side transmission device in the communication system according to claim 4. The communication system of the present invention can be realized.

  In the transmitter according to claim 10, when the modulation means used for data transmission is switched from the first modulation means to the second modulation means, the switch request generating means generates a switch request signal indicating that effect. Then, the generated switching request signal is superimposed on a part of the transmission signal output from the first modulation means.

  Therefore, if this transmission device is used as the transmission device in the communication system according to claim 1 or the master-side transmission device in the communication system according to claim 4, the same effect as in claim 2 is obtained. Can be obtained.

  Further, in the transmission device according to claim 11, the synchronization signal generation unit superimposes the synchronization signal on a part of the subcarrier output as the transmission signal from the first modulation unit, so that the first modulation is performed. The synchronization signal is transmitted from the means, and the switching request generation means changes the change pattern of the synchronization signal that is superimposed on a part of the subcarrier by the synchronization signal generation means, thereby transmitting the switching request signal.

  Therefore, if this transmission device is used as the transmission device in the communication system according to claim 1 or the master side transmission device in the communication system according to claim 4, the same effect as in claim 3 is obtained. Can be obtained.

  On the other hand, in the transmission device according to claim 12, the frame period of the transmission signal generated by the first modulation means is set to be shorter than the generation period of the noise component periodically generated around the communication system. Is done.

  Therefore, according to this transmission apparatus, the same effect as that of the fifth aspect can be obtained by using the transmission apparatus as the transmission apparatus of the communication system of the present invention (the master-side transmission apparatus in the fourth aspect).

In the transmission apparatus according to claim 13, when the first modulation unit generates the transmission signal, the frame period of the transmission signal is randomly changed.
Therefore, according to this transmission apparatus, the same effect as in the sixth aspect can be obtained by using the transmission apparatus as the transmission apparatus of the communication system according to the present invention (the master-side transmission apparatus in the fourth aspect).

  Further, in the transmitter according to claim 14, the frequency band of the noise component generated around the communication system among the subcarriers output as the transmission signal from the first modulation means is the synchronization signal generation means. The synchronization signal is superimposed on a plurality of subcarriers having a frequency difference larger than that of the subcarrier.

  Therefore, according to this transmission apparatus, the same effect as in the seventh aspect can be obtained by using the transmission apparatus as the transmission apparatus (the master-side transmission apparatus in claim 4) of the communication system of the present invention.

Next, the invention described in claims 15 to 17 is an invention relating to a receiving apparatus suitable for constructing the communication system of the present invention described above.
The receiver according to claim 15 comprises first orthogonal frequency division multiplexing first demodulation means, spread spectrum second demodulation means, and synchronization timing setting means, wherein the synchronization timing setting means comprises: A synchronization signal is extracted from the reception data restored by the demodulation means, and a synchronization timing necessary for the second demodulation means to restore the reception data from the reception signal is set based on the extracted synchronization signal.

  Therefore, according to the receiving device according to claim 15, the receiving device functions as the receiving device in the communication system according to claim 1 or the slave-side receiving device in the communication system according to claim 4. The communication system of the present invention can be realized.

  Next, in the receiving device according to claim 16, a switching request signal is extracted from the reception data restored by the first demodulating means, and data reception by the second demodulating means is started in accordance with the extracted switching request signal. Switching request determination means is provided.

  Therefore, if this receiving apparatus is used as the receiving apparatus in the communication system according to claim 1 or the master-side receiving apparatus in the communication system according to claim 4, the same effect as in claim 2 is obtained. Can be obtained.

  Further, in the receiver according to claim 17, the synchronization timing setting means sets the synchronization timing immediately after the demodulation means used for data reception is switched from the first demodulation means to the second demodulation means a plurality of times in the past. Estimated from the set synchronization timing.

  Therefore, this receiving apparatus can be used as the receiving apparatus (the slave-side receiving apparatus in claim 4) of the communication system of the present invention, and the same effect as in claim 8 can be obtained.

It is a block diagram showing the structure of the communication system of 1st Embodiment. It is a flowchart showing a synchronization timing determination process. It is a time chart explaining the transmission method of a synchronizing signal. It is a block diagram showing the structure of the communication system of 2nd Embodiment. It is a time chart explaining the transmission method of a switching request signal. It is a block diagram showing the structure of the communication system of 3rd Embodiment.

Embodiments of the present invention will be described below with reference to the drawings.
[First Embodiment]
The communication system of the present embodiment is for transmitting and receiving data between various electronic control units (ECUs) mounted on a vehicle via a power line L wired to the vehicle. As shown in FIG. The transmitter 10 is incorporated in the ECU 1 and the receiver 30 is incorporated in the ECU 2.

The transmission device 10 and the reception device 30 are connected to the power line L via the separation filters 3 and 4, respectively.
Separation filters 3 and 4 are for separating a DC voltage supplied from an in-vehicle battery (not shown) via a power line L and a communication signal (high frequency signal) for data communication, and are supplied from a DC power source. The DC voltage thus output is output to the power supply circuits 5 and 6 in the ECUs 1 and 2, and a communication signal is passed between the transmitter 10 and the receiver 30 and the power line L.

  The power supply circuits 5 and 6 generate a power supply voltage for driving the internal circuits of the ECUs 1 and 2 using a DC voltage supplied from the power line L via the separation filters 3 and 4, and transmit the generated power supply voltage. This is supplied to each internal circuit including the device 10 and the receiving device 30.

  Next, the transmission apparatus 10 includes an OFDM transmission unit 12, a DSSS transmission unit 14, and a DSSS synchronization signal generation unit 16, and a transmission unit used for data transmission according to a communication system switching request input from the outside. The OFDM transmission unit 12 and the DSSS transmission unit 14 are switched to each other.

  Here, first, the OFDM transmission unit 12 converts transmission data into a transmission signal by the OFDM method, and generates signal for baseband transmission (OFDM signal) by performing signal processing (IFFT or the like) on the transmission data. A processing unit 21 and a modulation unit 22 that generates a transmission signal for communication by modulating a carrier wave with the generated transmission signal are provided.

  Next, the DSSS transmission unit 14 converts transmission data into a transmission signal by a spread spectrum method (DSSS method) based on direct spreading (DS) using a spread code. The data processing unit 24 that generates the transmission signal of, the spreading unit 25 that multiplies the generated transmission signal and the spreading code output from the data processing unit 24, and the carrier wave is modulated by the output from the spreading unit 25 And a modulation unit 26 that generates a transmission signal for communication.

  Further, the DSSS synchronization signal generation unit 16 obtains a spreading cycle (in other words, a spreading code cycle) when generating a transmission signal from the data processing unit 24 of the DSSS transmission unit 14, and spreads and starts spreading. By generating a synchronization signal representing timing and passing the generated synchronization signal to the data processing unit of the OFDM transmission unit 12, two subcarriers constituting the transmission signal (OFDM signal) generated by the OFDM transmission unit 12 are generated. A synchronization signal is superimposed.

  That is, the DSSS synchronization signal generation unit 16 inserts the synchronization signal into the transmission data input to the OFDM transmission unit 12, so that the two subcarriers of the transmission signal (OFDM signal) output from the OFDM transmission unit 12 are inserted. The synchronization signal is superimposed, and thereafter, when data transmission by the DSSS transmission unit 14 is started, data reception can be started without performing synchronization acquisition on the receiving device 30 side.

Here, the two subcarriers used for transmitting the synchronization signal are set based on the frequency characteristics of the vehicle noise superimposed on the power line L.
That is, as shown in FIG. 3, vehicle noise that affects data communication using the OFDM transmitter 12 is periodically generated at a time interval of, for example, 1 ms (see “time characteristics” shown in FIG. 3). The frequency band is, for example, 5 MHz (see “frequency characteristics” shown in FIG. 3).

  For this reason, when vehicle noise occurs, normal data transmission cannot be performed on subcarriers whose frequency overlaps the frequency band of vehicle noise among subcarriers constituting a transmission signal (OFDM signal), and “communication failure” occurs. It becomes.

  Therefore, in this embodiment, two subcarriers having a frequency difference equal to or higher than the vehicle noise frequency band (5 MHz in FIG. 3) are set as the synchronization signal transmission subcarriers, and the synchronization signal is superimposed on the two subcarriers. The synchronization signal is transmitted by performing (specifically, amplitude modulation of the subcarrier by the synchronization signal which is a binary signal).

As a result, when vehicle noise occurs, even if one of the subcarriers becomes “communication failure”, the synchronization signal can be transmitted using the other subcarrier.
Also, as shown in FIG. 3, when the vehicle noise occurrence time overlaps with the preamble portion at the beginning of the transmission frame, the receiving device 30 cannot restore data from the received signal, so “communication failure” for each frame. It becomes.

  Therefore, in this embodiment, when the data processing unit 21 generates a transmission signal from transmission data, several types are set such that the frame period of the transmission signal is shorter than the vehicle noise generation period (1 ms in FIG. 3). The frame period is selected and set randomly.

As a result, it is possible to reduce the probability that the generation time of the vehicle noise overlaps with the preamble portion at the head of the transmission frame and “communication failure” occurs for each frame.
Next, the receiving device 30 includes an OFDM receiving unit 32, a DSSS receiving unit 34, and a DSSS synchronization timing determining unit 36, and according to a communication system switching request input from the outside, the receiving unit used for data reception is It is configured to switch to either the OFDM receiver 32 or the DSSS receiver 34.

  Here, first, the OFDM receiver 32 receives a transmission signal from the OFDM transmitter 12 of the transmitter 10 and restores received data from the received signal, and converts the received signal into a baseband OFDM signal. A demodulator 41 and a data processor 42 that restores received data by signal processing the output from the demodulator 41 are provided.

  Next, the DSSS receiving unit 34 receives a transmission signal from the DSSS transmission unit 14 of the transmission device 10 and restores received data from the received signal, and demodulates the received signal into a baseband received signal. Unit 44, a despreading unit 45 that multiplies the output from demodulating unit 44 and the despreading code, and a data processing unit 46 that restores received data by signal processing the output from despreading unit 45. The despread code is output from the data processing unit 46.

  Further, the DSSS synchronization timing determination unit 36 takes in the synchronization signal superimposed on the above-described synchronization signal transmission subcarrier from the data processing unit 42 of the OFDM reception unit 32, and receives the received data in the DSSS reception unit 34 from the synchronization signal. Is set to a synchronization timing for synchronizing the restoration operation (restoration cycle by the despreading code) with the spreading cycle of the DSSS transmission unit 14, and is output to the data processing unit 46 of the DSSS reception unit 34.

  In other words, in the present embodiment, the DSSS synchronization timing determination unit 36 executes the synchronization timing determination process shown in FIG. 2 so that the data processing unit 46 applies the despread code when the DSSS reception unit 34 starts data reception. The output timing is set as the synchronization timing, so that the data reception by the DSSS receiver 34 can be started promptly without performing the above-described synchronization acquisition.

Hereinafter, the synchronization timing determination process executed by the DSSS synchronization timing determination unit 36 will be described.
The synchronization timing determination process shown in FIG. 2 is a process that is repeatedly executed when data is received by the OFDM receiver 32. When the process is started, first, in S110 (S represents a step), the data processor 42 starts the process. By determining whether or not a synchronization signal has been input, the data processor 42 waits for the synchronization signal superimposed on at least one of the synchronization signal subcarriers to be extracted.

  In S110, when it is determined that the synchronization signal is input from the data processing unit 42 (in other words, the synchronization signal is extracted), the process proceeds to S120, and the signal level of the synchronization signal (specifically, the synchronization signal is described in detail). It is determined whether or not the signal level of the signal transmission subcarrier exceeds a threshold value.

  If it is determined in S120 that the signal level of the synchronization signal exceeds the threshold value, the process proceeds to S130, and the timing (time) when the synchronization signal is input from the data processing unit 42 is used as the synchronization timing. It memorize | stores in memory (not shown), and transfers to S140.

  If it is determined in S120 that the signal level of the synchronization signal does not exceed the threshold value, the synchronization signal extracted by the data processing unit 42 is likely to be noise, and the process proceeds to S140 as it is. .

  In S140, it is determined whether or not a command for switching the communication method from the OFDM method to the DSSS method is input based on a switching request signal input from the outside. If the command for switching to the DSSS method is not input, The process proceeds to S110, and if a switching command to the DSSS system is input, the process proceeds to S150.

  In S150, the next synchronization timing (in other words, the first synchronization timing after switching to the communication method) is estimated from the past synchronization timings stored in the processing of S130. In S160, the estimated synchronization timing is calculated. The data is output to the data processing unit 46, and the process ends.

The synchronization timing is estimated, for example, by calculating the next synchronization timing so that the synchronization timing interval becomes a past average value.
When the synchronization timing calculated in this way is output to the data processing unit 46, the data processing unit 46 starts outputting the despread code at the synchronization timing and continues to output the despread code repeatedly. Thus, the despreading unit 45 sequentially processes (despreads) the received signal, and restores the transmission data from the DSSS transmission unit 14.

  As described above, in the communication system according to the present embodiment, when the transmission device 10 performs data transmission via the OFDM transmission unit 12, the DSSS synchronization signal generation unit 16 in the transmission device 10 includes the DSSS transmission unit. 14 obtains a transmission cycle (spreading cycle) in the DSSS system from the 14 data processing units 24, generates a synchronization signal indicating the spreading cycle and spreading start timing, and uses the generated synchronization signal as data processing of the OFDM transmission unit 12. The synchronization signal is transmitted from the OFDM transmitter 12 by outputting to the unit 21.

  On the receiving device 30 side, when data is received by the OFDM receiving unit 32, the DSSS synchronization timing determining unit 36 takes the synchronization signal from the data processing unit 42 and sets the synchronization timing necessary for restoring the received data in the DSSS scheme. When the communication method is switched from the OFDM method to the DSSS method, the first synchronization timing after switching the communication method is estimated from the plurality of synchronization timings calculated a plurality of times in the past based on the synchronization signal, and the DSSS receiving unit 34 Output.

  As a result, when the communication system is switched from the OFDM system to the DSSS system, the DSSS receiving unit 34 can start data reception promptly without performing synchronization acquisition.

  That is, as described at the bottom of FIG. 3, in the conventional receiving apparatus, when the communication method is switched from the OFDM method to the DSSS method at time T0, in order to synchronize the despread code with the spread code on the transmission side, Synchronization acquisition is performed using the number of spreading code cycles of the reception signal, and reception data is sequentially restored from the reception signal with reference to the synchronization timing obtained by the synchronization acquisition.

  For this reason, according to the conventional communication system, the time required for synchronization acquisition to be completed after the communication system is switched to the DSSS system (= spread code period × number of codes × number of samples per chip × number of synchronization acquisition repetitions) ), The start of communication by the DSSS method is delayed.

  However, according to the communication system of this embodiment, when the communication method is switched from the OFDM method to the DSSS method at time T0 in the receiving device 30, the synchronization timing immediately after the switching is synchronized with the synchronization transmitted from the transmitting device 10. Since the data reception is estimated based on the signal, the synchronization acquisition time necessary for the synchronization acquisition on the receiving device 30 side can be eliminated, and the data communication by the DSSS method can be started promptly.

  In the present embodiment, the transmission of the synchronization signal from the transmission device 10 to the reception device 30 includes a frequency band (for example, 5 MHz) of vehicle noise that affects data communication among a large number of subcarriers constituting the OFDM signal. Since two subcarriers having a larger frequency difference are used, it is possible to prevent the synchronization signal from being transmitted due to vehicle noise.

  In addition, when vehicle noise is generated when the vehicle noise is transmitted through the preamble portion of the transmission frame, the reception device 30 may cause a “communication failure” for each frame. The frame period of the signal is randomly selected from several types of frame periods set to a period shorter than the generation period of vehicle noise (for example, 1 ms). Thus, it is possible to prevent the synchronization signal from being transmitted from the transmission apparatus 10 to the reception apparatus 30 by reducing the probability of overlapping with the preamble portion of the transmission apparatus 10.

In the present embodiment, the OFDM transmitter 12 constituting the transmitter 10 corresponds to the first modulator of the present invention, and the DSSS transmitter 14 corresponds to the second modulator of the present invention. The synchronization signal generation unit 16 corresponds to the synchronization signal generation means of the present invention. Further, the OFDM receiver 32 constituting the receiving device 30 corresponds to the first demodulator of the present invention, the DSSS receiver 34 corresponds to the second demodulator of the present invention, and the DSSS synchronization timing determiner 36 This corresponds to the synchronization timing setting means of the present invention.
[Second Embodiment]
Next, a second embodiment of the present invention will be described.

  As shown in FIG. 4, the communication system of the present embodiment is basically configured in the same manner as the communication system of the first embodiment described above. The difference from the first embodiment is that the ECU 1 determines the transmission method. The transmitter 7 is provided with a DSSS request signal generator 18, and the receiver 30 is provided with a DSSS request determination unit 38.

Hereinafter, this difference will be described.
In the first embodiment, the transmission method switching request is input to the transmission device 10 and the reception device 30 from the outside. However, in the present embodiment, the transmission method determination unit in the ECU 1 provided with the transmission device 10. 7 determines whether the transmission unit used for data transmission is the OFDM transmission unit 12 or the DSSS transmission unit 14 from the content of transmission data (for example, importance), and when it is necessary to switch the transmission unit Then, a switching request is input to the transmission device 10.

  The transmission method determination unit 7 selects, for example, an OFDM method capable of high-speed communication when the transmission data is normal data that does not cause a problem even if communication fails (in other words, can be covered by retransmission). When the transmission data is important data that requires certainty of communication (for example, important data necessary for vehicle control), a DSSS method that is less susceptible to vehicle noise is selected.

  For this reason, in the transmission device 10, in response to a switching request from the transmission method determination unit 7, not only the transmission unit used for data transmission is switched to either the OFDM transmission unit 12 or the DSSS transmission unit 14, but also reception. It is necessary to notify the device 30 of a request for switching the communication method.

  For this purpose, as described in Patent Document 1, information indicating a communication mode switching request is included in the transmission data from the transmission device 10 to notify the reception device 30 of the switching of the communication method. May be.

  However, in such a notification method, it is necessary to analyze the received data on the receiving device 30 side to determine a communication system switching request, and this determination takes time. For this reason, the transmission apparatus 10 and the reception apparatus 30 are provided with the DSSS synchronization signal generation section 16 and the DSSS synchronization timing determination section 36 so that important data can be transmitted and received immediately after the communication system is switched to the DSSS system. The start of transmission / reception of important data will be delayed.

Therefore, the communication system of the present embodiment is
(1) When a request for switching to the DSSS system of the communication system is generated on the transmitting apparatus 10 side, the DSSS request signal generating unit 18 generates a switching request signal indicating that fact and the data of the OFDM transmitting unit 12 By outputting to the processing unit 21, the switching request signal is superimposed on one of the subcarriers of the OFDM signal generated by the data processing unit 21,
(2) On the receiving device 30 side, the DSSS request determination unit 38 acquires a switching request signal from the data processing unit 42 of the OFDM receiving unit 32 to determine a switching request to the DSSS method of the communication method, and the DSSS Activate the data processing unit 46 of the receiving unit 34;
It is configured as follows.

  As a result, the receiving apparatus 30 side promptly detects a request to switch to the DSSS scheme generated on the transmitting apparatus 10 side, and switches the receiving unit used for data reception from the OFDM receiving unit 32 to the DSSS receiving unit 34. Will be able to.

  In the present embodiment, the DSSS request signal generation unit 18, like the DSSS synchronization signal generation unit 16, superimposes the switching request signal on two subcarriers having a frequency difference larger than the vehicle noise frequency band. This prevents the switching request signal from being transmitted due to vehicle noise.

  Here, as shown in FIG. 5A, the DSSS request signal generation unit 18 uses a subcarrier different from the subcarrier used by the DSSS synchronization signal generation unit 16 to transmit the synchronization signal. It can be configured to transmit a signal.

  However, if the synchronization signal and the switching request signal are transmitted using different subcarriers as described above, four subcarriers are required for transmission of these signals, and data transmission is performed by the amount of the four subcarriers. There will be fewer available subcarriers.

  Therefore, as shown in FIG. 5B, the DSSS request signal generation unit 18 changes the synchronization signal by inverting the output from the DSSS synchronization signal generation unit 16 when a switching request is generated, for example. The pattern may be changed.

  In this way, the switching request signal and the synchronization signal can be transmitted using the same subcarrier, and the number of subcarriers used for transmitting the synchronization signal and the switching request signal. Can be reduced by half to prevent the communication speed in the OFDM system from being lowered.

In the present embodiment, the DSSS request signal generation unit 18 corresponds to the switching request generation unit of the present invention, and the DSSS request determination unit 38 corresponds to the switching request determination unit of the present invention.
[Third Embodiment]
Next, a third embodiment of the present invention will be described.

  As shown in FIG. 6, in the communication system of the present embodiment, the ECUs 1 and 2 are provided with communication devices 8 and 9 capable of bidirectional communication via the power line L, and the communication device 8 serves as a master on the slave side. This is a master-slave communication system in which data is transmitted to the communication device 9 and the slave communication device 9 transmits (replies) data in response to data transmission from the master communication device 8.

  The communication device 8 on the master side includes a transmission device 10 for transmitting data to the communication device 8 on the slave side, a reception device 60 for receiving a transmission signal from the communication device 9 on the slave side, There is provided a directional coupler (circulator or the like) 50 that outputs an output (transmission signal) from the transmission device 10 to the separation filter 3 side and inputs an input (reception signal) from the separation filter 3 to the reception device 60. Yes.

  The slave communication device 9 includes a reception device 30 for receiving a transmission signal from the master communication device 8, a transmission device 80 for transmitting data to the master communication device 8, and There is provided a directional coupler (circulator or the like) 52 that outputs an output (transmission signal) from the transmission device 80 to the separation filter 4 side and inputs an input (reception signal) from the separation filter 4 to the reception device 30. .

  Here, the transmission device 10 provided in the communication device 8 on the master side and the reception device 30 provided in the communication device 9 on the slave side are respectively the transmission device 10 and the reception device 30 described in the first embodiment. Since the configuration is the same, a description thereof will be omitted. Next, the transmission device 80 provided in the slave communication device 9 and the reception device 60 provided in the master communication device 8 will be described.

  First, the transmission device 80 on the slave side includes an OFDM transmission unit 82 and a DSSS transmission unit 84. According to a communication system switching request input from the outside, the transmission unit used for data transmission is divided into the OFDM transmission unit 82 and the DSSS. It is configured to switch to any one of the transmission unit 84.

  The OFDM transmission unit 82 includes a data processing unit 91 and a modulation unit 92 as in the master-side OFDM transmission unit 82, and the DSSS transmission unit 84 includes a data processing unit as in the master-side DSSS transmission unit 14. 94, a diffusion unit 95, and a modulation unit 96.

  Next, the receiving device 60 on the master side includes an OFDM receiving unit 62 and a DSSS receiving unit 64. In accordance with a communication method switching request input from the outside, the receiving unit used for data reception is referred to as an OFDM receiving unit 62. It is configured to switch to either one of the DSSS receiving unit 64.

  The OFDM receiving unit 62 includes a demodulating unit 71 and a data processing unit 72 as in the slave-side OFDM receiving unit 32, and the DSSS receiving unit 64 is similar to the demodulating unit in the slave-side DSSS receiving unit 34. 74, a despreading unit 75, and a data processing unit 76.

  In the DSSS transmission unit 84 on the slave side, the data processing unit 94 determines the output timing of the spread code based on the synchronization timing output from the DSSS synchronization timing determination unit 36 when switching the communication method to the DSSS method. A synchronization signal is generated, and at the time of data transmission, transmission data is converted (modulated) into a transmission signal in accordance with the synchronization signal.

  Further, in the DSSS receiving unit 64 on the master side, the data processing unit 76 is configured to take in a synchronization signal representing the synchronization timing of the DSSS transmission unit 14 from the DSSS synchronization signal generating unit 16 and restore the received data.

  For this reason, in the present embodiment, the DSSS transmitters 14 and 84 and the DSSS receivers 34 and 64 used for transmitting and receiving data by the DSSS method synchronize the spreading code and the despreading code used at the time of transmission and reception. Therefore, the synchronization signal (synchronization timing) can be matched.

  Therefore, according to the present embodiment, when the communication method for performing data communication between the communication devices 8 and 9 is switched from the OFDM method to the DSSS method, and when the DSSS receivers 34 and 64 start data reception, Thus, data reception can be started promptly without performing synchronization acquisition.

  In this embodiment, the OFDM transmitter 82 provided in the slave-side transmitter 80 corresponds to the third modulator of the present invention, and the DSSS transmitter 84 is also used as the fourth modulator of the present invention. Equivalent to. The OFDM receiver 62 provided in the master-side receiver 60 corresponds to the third demodulator of the present invention, and the DSSS receiver 64 similarly corresponds to the fourth demodulator of the present invention.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, A various aspect can be taken in the range which does not deviate from the summary of this invention.
For example, in the above embodiment, the communication system is described as performing data communication using the power line L wired to the vehicle. However, the present invention is a communication system performing data communication using a communication line dedicated for communication. Even if it exists, it can apply even if it is a communication system which performs radio | wireless communication, It can apply even if it is a communication system constructed | assembled in the place different from a vehicle.

  When the transmission device 10 and the reception device 30 perform data communication using a communication line dedicated for communication, the transmission device 10 and the reception device 30 are provided with separation filters 3 and 4 between the communication lines. Instead, it may be connected directly to the communication line (in the case of the third embodiment, via the directional couplers 50 and 52), and the power line L may be directly connected to the power supply circuits 5 and 6.

  In addition, when the transmission device 10 and the reception device 30 perform data communication by wireless communication, an amplifier circuit that amplifies a transmission signal and a transmission antenna are sequentially connected to the transmission device 10 instead of the separation filter 3. Then, the transmission signal amplified by the amplifier circuit is radiated as a transmission radio wave from the transmission antenna, and the reception device 30 side has a reception antenna that receives the transmission radio wave from the transmission antenna instead of the separation filter 4. An amplification circuit that amplifies a reception signal from the reception antenna and inputs the amplified signal to the reception device 30 may be provided, and the power line L may be directly connected to the power supply circuits 5 and 6.

  In the above-described embodiment, the direct spread (DS) method has been described as an example of the spread spectrum method (SS method) communication. However, in the present invention, frequency hopping (FH) that performs spread spectrum using a hopping pattern is described. ) Method or a hybrid method combining the DS method and the FH method can be applied in the same manner as in the above embodiment to obtain the same effect.

  In the above embodiment, when the communication method is the OFDM method, when transmitting the synchronization signal (or the synchronization signal and the switching request signal) from the transmission device 10 to the reception device 30, the subcarriers constituting the OFDM signal are transmitted. In the above description, it is assumed that two subcarriers having a frequency difference larger than the frequency band of vehicle noise are used. However, the number of subcarriers used for transmission of the synchronization signal (or the synchronization signal and the switching request signal) is the ambient noise. It may be set as appropriate in consideration of the influence of the above, and may be one or three or more.

  DESCRIPTION OF SYMBOLS 1, 2 ... ECU (electronic control apparatus), 3, 4 ... Separation filter, 5, 6 ... Power supply circuit, L ... Power line, 7 ... Transmission method determination part, 8, 9 ... Communication apparatus, 10, 80 ... Transmission apparatus, DESCRIPTION OF SYMBOLS 12,82 ... OFDM transmission part, 14,84 ... DSSS transmission part, 16 ... DSSS synchronous signal generation part, 18 ... DSSS request signal generation part, 21,24,91,94 ... Data processing part, 22,26,92 , 96 ... Modulation section, 25, 95 ... Spreading section, 30, 60 ... Receiver, 32, 62 ... OFDM reception section, 34, 64 ... DSSS reception section, 36 ... DSSS synchronization timing determination section, 38 ... DSSS request determination section , 41, 44, 71, 74 ... demodulator, 42, 46, 72, 76 ... data processor, 45, 75 ... despreader.

Claims (17)

As a modulation means for converting transmission data into a transmission signal, a first modulation means of an orthogonal frequency division multiplexing method and a second modulation means of a spread spectrum method are provided, and the modulation means used for transmission of the transmission data includes the first modulation means. A transmission device configured to be switchable between one modulation means and the second modulation means;
As a demodulating means for receiving a transmission signal from the transmission apparatus and restoring received data from the received signal, an orthogonal frequency division multiplexing method for restoring transmission data transmitted from the transmission apparatus via the first modulation means is used. A receiving apparatus comprising: a first demodulating means; and a second spread spectrum system demodulating means for restoring transmission data transmitted from the transmitting apparatus via the second modulating means;
In a communication system comprising:
The transmission apparatus generates a synchronization signal representing a spreading period when the second modulation unit converts the transmission data into a transmission signal, and the synchronization signal is transmitted to the transmission signal output from the first modulation unit. Provided with a synchronization signal generating means to be superimposed on the part,
The receiver extracts the synchronization signal from the reception data restored by the first demodulation means, and the second demodulation means restores the reception data from the reception signal based on the extracted synchronization signal. A communication system comprising synchronization timing setting means for setting a synchronization timing necessary for the operation. When the modulation means used for data transmission is switched from the first modulation means to the second modulation means, the transmission device generates a switching request signal indicating that fact, and the generated switching request signal is sent to the first modulation means. Switching request generating means for superimposing on a part of the transmission signal output from one modulation means;
The receiving apparatus extracts the switching request signal from the reception data restored by the first demodulating means, and starts switching data reception by the second demodulating means in accordance with the extracted switching request signal. The communication system according to claim 1, further comprising: The synchronization signal generation unit causes the synchronization signal to be transmitted from the first modulation unit by superimposing the synchronization signal on a part of the subcarrier output as a transmission signal from the first modulation unit,
The switching request generation unit causes the switching request signal to be transmitted by changing a change pattern of a synchronization signal superimposed on a part of the subcarrier by the synchronization signal generation unit. Communication system. Consists of a plurality of communication devices, one of the communication devices becomes a master communication device, transmits a signal to another slave communication device, and the slave communication device returns a signal from the master communication device A master-slave communication system,
The master side communication device is:
As a modulation means for converting transmission data to the slave side communication device into a transmission signal, a first modulation means of an orthogonal frequency division multiplexing system and a second modulation means of a spread spectrum system are provided and used for transmission of the transmission data The modulation means for switching is configured to be switchable between the first modulation means and the second modulation means, and further, a spreading period when the second modulation means converts transmission data into a transmission signal is set. A master-side transmission device having a synchronization signal generation unit that generates a synchronization signal to be expressed and superimposes the synchronization signal on a part of the transmission signal output from the first modulation unit;
With
The slave side communication device is:
Orthogonal frequency for restoring transmission data transmitted from the master side transmission device via the first modulation means as demodulation means for receiving a transmission signal from the master side transmission device and restoring received data from the received signal A first division means for demodulating multiplexing; and a second spread spectrum method for restoring transmission data transmitted from the master side transmission apparatus via the second modulation means, and further comprising the first demodulation means. The synchronization signal is extracted from the reception data restored by the demodulation means, and the synchronization timing necessary for the second demodulation means to restore the reception data from the reception signal is set based on the extracted synchronization signal A slave-side receiving device having a synchronization timing setting means,
As modulation means for converting transmission data to the master side communication device into transmission signals, the third modulation means of the orthogonal frequency division multiplexing system and the synchronization timing of the second demodulation means set by the synchronization timing setting means Spread spectrum fourth modulation means for synchronously converting transmission data into a transmission signal, and the modulation means used for transmission of the transmission data is either the third modulation means or the fourth modulation means A slave-side transmitter configured to be switchable to
With
Furthermore, in the master side communication device,
Orthogonal frequency for restoring transmission data transmitted from the slave side transmission device via the third modulation unit as demodulation means for receiving a transmission signal from the slave side transmission device and restoring received data from the received signal Spread spectrum that restores transmission data transmitted from the slave side transmission device via the fourth modulation means in synchronization with the third demodulation means of the division multiplexing system and the synchronization signal generated by the synchronization signal generation means A master side receiving device comprising a fourth demodulating means
A communication system characterized in that is provided.   The frame period of the transmission signal generated by the first modulation means is shorter than the generation period of noise components periodically generated around the communication system. The communication system according to item.   6. The communication system according to claim 5, wherein the first modulation unit randomly changes the frame period when generating the transmission signal.   The synchronization signal generation means includes a plurality of subcarriers having a frequency difference larger than a frequency band of a noise component generated around the communication system, out of the subcarriers output as a transmission signal from the first modulation means. The communication system according to claim 1, wherein the synchronization signal is superimposed.   The synchronization timing setting means estimates the synchronization timing immediately after the demodulating means used for data reception is switched from the first demodulating means to the second demodulating means from the synchronization timing set a plurality of times in the past. The communication system according to any one of claims 1 to 7. As a modulation means for converting transmission data into a transmission signal, a first modulation means of an orthogonal frequency division multiplexing method and a second modulation means of a spread spectrum method are provided, and the modulation means used for transmission of the transmission data includes the first modulation means. In a transmission apparatus configured to be switchable between one modulation means and the second modulation means,
A synchronization signal that generates a synchronization signal representing a spreading period when the second modulation means converts the transmission data into a transmission signal and superimposes the synchronization signal on a part of the transmission signal output from the first modulation means A transmission apparatus comprising generation means.   When switching the modulation means used for data transmission from the first modulation means to the second modulation means, a switching request signal indicating that is generated, and the generated switching request signal is output from the first modulation means. The transmission apparatus according to claim 9, further comprising switching request generation means for superimposing the transmission signal on a part of the transmission signal. The synchronization signal generation unit causes the synchronization signal to be transmitted from the first modulation unit by superimposing the synchronization signal on a part of the subcarrier output as a transmission signal from the first modulation unit,
The switching request generation unit causes the switching request signal to be transmitted by changing a change pattern of a synchronization signal superimposed on a part of the subcarrier by the synchronization signal generation unit. Transmitter.   12. The frame period of a transmission signal generated by the first modulation unit is shorter than a generation period of noise components periodically generated around the communication system. The transmitter according to the item.   13. The transmission apparatus according to claim 12, wherein the first modulation unit randomly changes the frame period when generating the transmission signal.   The synchronization signal generation means includes a plurality of subcarriers having a frequency difference larger than a frequency band of a noise component generated around the communication system, out of the subcarriers output as a transmission signal from the first modulation means. The transmission apparatus according to claim 9, wherein the synchronization signal is superimposed. As a demodulating means for restoring received data from a received signal, a receiving apparatus comprising a first demodulating means of orthogonal frequency division multiplexing and a second demodulating means of spread spectrum system,
The synchronization signal is extracted from the received data restored by the first demodulating means, and the synchronization necessary for the second demodulating means to restore the received data from the received signal based on the extracted synchronizing signal. A receiving apparatus comprising synchronization timing setting means for setting timing.   A switching request determination unit is provided for extracting a switching request signal from the received data restored by the first demodulating unit and starting data reception by the second demodulating unit according to the extracted switching request signal. The receiving device according to claim 15.   The synchronization timing setting means estimates the synchronization timing immediately after the demodulating means used for data reception is switched from the first demodulating means to the second demodulating means from the synchronization timing set a plurality of times in the past. The receiving device according to claim 15 or 16.