JP2007335959A - Wireless station in dedicated short range communication and transmission method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dedicated short range communications (DSRC) in which an on-vehicle apparatus needs to be adaptable to the ASK modulation system and the π/4 shift QPSK modulation system and when a transmission circuit block such as a power amplifier is shared between both modulation systems, transmission output powers can be set to optimum values in the respective modulation systems. <P>SOLUTION: A wireless station in the dedicated short range communications is provided with a switching means so that gain of the power amplifier or an attenuation of an attenuator between both modulation systems can be switched. As the switching means, a digital potentiometer whose resistance can be varied by an electric control signal or an analog switch or the like which is switched by an electric control signal is used. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radio communication station and its radio station in a dedicated short range communications (DSRC) using two types of ASK (Amplitude Shift Keying) modulation method and π / 4 shift QPSK (Quadrature Phase Shift Keying) modulation method. It relates to the transmission method.

  In a system in which a mobile station and a base station perform radio communication, when a modulation scheme used for communication is selected from a plurality of predetermined modulation schemes, the modulation / demodulation circuit of the mobile station or base station It becomes necessary to support the modulation method.

  For example, with respect to DSRC in which a vehicle-mounted device installed in a vehicle and a roadside device installed on the roadside perform wireless communication, there are ASK modulation method and π / 4 shift QPSK modulation method as a modulation method. The modulation method is determined based on the roadside machine. Therefore, the vehicle-mounted device needs to support both ASK and π / 4 shift QPSK.

  Here, in the wireless communication of the narrow area communication system, the output power transmitted from the roadside device and the vehicle-mounted device reaches the communication partner at the electric field level that can be received by each other as long as the vehicle-mounted device is within the specified communication area. You need to set that level. For example, considering the situation where the vehicle-mounted device receives the roadside device's transmission radio waves, the stronger the radio waves emitted by the roadside device (within the standard), the wider its communication area, but directly below the roadside device antenna. The radio field intensity is too strong. Conversely, the weaker the radio wave emitted by the roadside device (within the standard), the narrower the communication area. That is, it is desirable that the output power transmitted between the roadside device and the vehicle-mounted device is strong enough to realize communication regardless of whether the communication distance between road vehicles is long or short.

  Here, there is a problem that the relationship between the communication distance and the radio wave level is different between the ASK modulation method and the π / 4 shift QPSK modulation method handled in the narrow area communication system. That is, in the case of the ASK modulation method that handles amplitude information, the envelope level of the modulated wave varies according to the information, and the average power level is lower than the carrier power level. Specifically, if the on / off duty of the ASK modulation signal is 50%, the average power level is about ½ of the carrier power level. On the other hand, in the case of the π / 4 shift QPSK modulation method that handles phase information, if some amplitude fluctuations that occur at the phase change point are ignored, the envelope of the modulated wave is constant and the average power level is the carrier power level. It becomes equivalent.

  Thus, the ASK modulation method and the π / 4 shift QPSK modulation method have different characteristics regarding the power level.

  In order to simply configure the ASK and π / 4 shift QPSK modulation / demodulation circuit, for example, Patent Document 1 describes means for simplifying the modulation / demodulation circuit of both modulation systems. This is because the transmission circuit blocks such as a power amplifier and a quadrature modulator are used in common by switching the baseband signal (I channel signal, Q channel signal) in each of the two types of modulation methods. It is possible to achieve miniaturization. However, when the transmission circuit block is shared, it is assumed that the power level transition of the transmission signal in the transmission circuit block is also common. That is, in each modulation method, the transmission output power cannot be set individually, and the relationship between the communication distance and the radio wave level is different.

JP 2004-147052 A

  With regard to a narrow-area communication system in which an on-vehicle device installed in a vehicle and a roadside device installed on the roadside perform wireless communication, there are an ASK modulation method and a π / 4 shift QPSK modulation method as a modulation method. The modulation method is determined based on the other roadside machine. Therefore, the vehicle-mounted device needs to support both ASK and π / 4 shift QPSK, but the characteristics regarding the power level are different between the two modulation methods. Specifically, in the case of the ASK modulation method that handles amplitude information, the envelope level of the modulated wave varies according to the information, and the average power level is lower than the carrier power level. On the other hand, in the case of the π / 4 shift QPSK modulation system that handles phase information, the envelope of the modulation wave is constant and the average power level is the carrier power if the slight amplitude fluctuation generated at the phase change point is ignored. Equivalent to level. As described above, the ASK modulation method and the π / 4 shift QPSK modulation method have a problem that the characteristics regarding the power level are different.

  Here, in order to realize the modulation / demodulation of both the modulation schemes, it is desirable to share the transmission circuit block such as a power amplifier in both the modulation schemes as much as possible in consideration of the cost and the size. However, in this case, it is premised that the power level transition of the transmission signal in the shared transmission circuit block is also common, and there is a problem that the transmission output power cannot be individually set in each modulation method.

  The present invention deals with an ASK modulation method and a π / 4 shift QPSK modulation method, and in a narrow area communication system radio station that shares a power amplifier circuit for amplifying the power of a transmission signal for the above two types of modulation methods. Switching means for switching the output power is provided.

  The present invention also deals with an ASK modulation method and a π / 4 shift QPSK modulation method, and in a narrow area communication system radio station sharing a power amplification circuit for amplifying the power of a transmission signal for the two types of modulation methods. Switching means for switching the transmission output power and means for selecting the magnitude of the transmission output power by the switching means according to which of the two types of transmission is used are provided.

  In a preferred embodiment of the present invention, switching means for switching the gain of the power amplifier is provided, and as the switching means, a digital potentiometer whose resistance value can be varied by an electrical control signal is provided.

  In a preferred embodiment of the present invention, there is provided switching means for switching the attenuation amount of the attenuator provided at the front stage or the rear stage of the power amplifier, and as the switching means, a digital value whose resistance value can be varied by an electrical control signal. A potentiometer is provided.

  In another preferred embodiment of the present invention, an analog switch that can be switched by an electrical control signal is provided.

  According to the present invention, in a radio station of a narrow-area communication system that handles an ASK modulation scheme and a π / 4 shift QPSK modulation scheme, low cost by sharing a transmission circuit block such as a power amplifier in both the modulation schemes as much as possible, and Miniaturization can be realized.

  In addition to this, transmission processing can be performed without performance degradation by optimally setting the transmission output power individually in both the modulation schemes.

  Furthermore, the processing algorithm and the additional circuit are simple, there is no large cost and no increase in circuit scale, the communication reliability is increased, and the communication error rate can be reduced.

  Other objects and features of the present invention will become apparent from the following description of the embodiments.

  Preferred embodiments of the present invention will be described with reference to the drawings. The present embodiment is an example of a DSRC system in which a vehicle-mounted device installed in a vehicle and a roadside device installed on the roadside perform wireless communication, and relates to a transmission circuit on the vehicle-mounted device side of the DSRC system.

  FIG. 1 is a schematic view of an in-vehicle device and a roadside device of a DSRC system according to an embodiment of the present invention performing wireless communication as viewed from the inside of a vehicle. In this example, the vehicle-mounted device 11 of the DSRC system is installed on the dashboard 12. In this example, since the vehicle-side antenna is assumed to be integrated with the vehicle-mounted device, the installation position of the vehicle-mounted device 11 is on the dashboard 12. However, if the vehicle-mounted device 11 and the antenna are separated from each other. In the case of the type, it is sufficient to install only the antenna on the dashboard 12. In this case, there is no restriction | limiting in the installation position of the onboard equipment 11. FIG. In this case, the antenna position is not particularly limited, and may be attached to the windshield according to the specifications. In addition, usability can be improved by linking the car navigation system 13 and the DSRC in-vehicle device 11. However, in that case, it is a premise that the DSRC vehicle-mounted device 11 and the car navigation system 13 have interfaces that can communicate with each other. On the other hand, the roadside unit 14 has an antenna directed toward the vehicle passing therethrough, and the vehicle enters the communication area created by the roadside antenna and communication is started. Reference numerals 15 and 16 denote transmission / reception radio waves.

  FIG. 2 shows a system block diagram of the vehicle-mounted device of the DSRC system according to one embodiment of the present invention. Wireless communication with the roadside device is performed via the antenna 21. The high-frequency transmitter / receiver 22 is mainly composed of a transmission circuit and a reception circuit. The transmission circuit modulates data and the reception circuit demodulates data. Baseband signal processing is performed by the modem 23. The on-board device of the DSRC system includes an HMI (Human Machine Interface) 25 and an IC card interface 26 in addition to the control processing unit 24 that performs overall control of the on-vehicle device. Further, as described above, the vehicle-mounted device of the DSRC system can be connected to a car navigation system or built in the car navigation system in order to improve usability in the vehicle, and has an interface 27 for that purpose.

  Here, as described above, the relationship between the communication distance and the radio wave level is different between the ASK modulation method and the π / 4 shift QPSK modulation method handled in the narrow area communication system. That is, in the case of the ASK modulation method that handles amplitude information, the envelope level of the modulated wave varies according to the information, and the average power level is lower than the carrier power level. On the other hand, in the case of the π / 4 shift QPSK modulation method that handles phase information, the envelope of the modulation wave is constant and the average power level is the carrier power level if some amplitude fluctuations occurring at the phase change point are ignored. Is equivalent to

  In a conventional circuit in which the circuit is shared by the ASK modulation method and the π / 4 shift QPSK modulation method, a quadrature modulator, an up-converter, a power amplifier, and a carrier wave, which will be described later in an embodiment of the present invention, are generated. The local oscillator is shared. In this circuit system, although the common carrier wave is used, the transmission output average power radiated from the antenna differs in each modulation system.

  Therefore, the present invention solves this problem by providing switching means for switching the transmission output power in the ASK modulation system and the π / 4 shift QPSK modulation system.

  FIG. 3 is a diagram showing a process flow of the DSRC on-vehicle device according to the embodiment of the present invention. First, in step 31, the vehicle-mounted device enters the DSRC communication zone created by the roadside device. Thereafter, in step 32, the vehicle-mounted device identifies the modulation method used for communication in accordance with the received wave from the roadside device. Specifically, it is determined whether the radio wave emitted from the roadside device is using the ASK modulation method or the π / 4 shift QPSK modulation method defined by DSRC. Therefore, it is necessary for the vehicle-mounted device to assume the reception of the above-described two modulation schemes at this point, and both the above-described two-modulation demodulation circuits are provided. Next, in step 33, the vehicle-mounted device switches the gain of the power amplifier based on the result of identifying the modulation method as described above. Or when the onboard equipment has an attenuator in the front | former stage or back | latter stage of a power amplifier, the attenuation amount is switched. The method for switching the power will be described later.

  When the switching is completed, the vehicle-mounted device next starts transmission processing in step 34. In addition, it is necessary to protect the time (within several tens of microseconds) defined in the DSRC system as the time from when the signal from the roadside device is received until the vehicle-mounted device completes transmission. That is, it is a condition that the switching of the gain of the power amplifier or the switching of the attenuation amount of the attenuator is completed within the above time.

  Next, switching of the gain of the power amplifier will be described with reference to FIGS.

  FIG. 4 is a block diagram showing a configuration of a narrow area communication system radio station according to an embodiment of the present invention. In the figure, the transmission / reception wave by the antenna 401 is guided to the transmission / reception changeover switch 403 through the band pass filter 402. At the time of reception, the changeover switch 403 is in a state where the upper side is connected as shown in the figure, and when the vehicle-mounted device enters the communication zone, the signal from the roadside device is received by the reception circuit block 404. This received data is either ASK received data or QPSK received data, and the modem 405 identifies the modulation method. The modem 405 transmits the modulation method identification result (ASK / QPSK signal) to the control processing unit 406.

  As a transmission side circuit, the output of the quadrature modulator 407 is converted into a high frequency signal by the local oscillator 408 and the up-converter 409, amplified by the variable gain power amplifier 410, and the changeover switch 403, the band-pass The data is transmitted from the antenna 401 to the outside via the filter 402.

  In this embodiment, a digital potentiometer 411 is used as means for switching the gain of the power amplifier 410. As described above, when the vehicle-mounted device enters the communication zone and the modulation scheme is identified by the reception circuit block 404 and the modem 405, the modulation scheme identification result is transmitted to the control processing unit 406. This signal may be, for example, a simple binary digital signal indicating Hi during ASK modulation and Lo during π / 4 shift QPSK modulation.

  Thereafter, the control processing unit 406 controls the resistance value of the digital potentiometer 411 based on the identification result. Specifically, the resistance voltage divider 4112 is digitally controlled by the digital control circuit 4111 in the digital potentiometer 411. In this embodiment, the control of the digital potentiometer 411 by the control processing unit 406 is realized by a serial interface with three terminals of DATA (data), CLK (clock), and CS (chip select). However, this method is not necessarily required if the resistance value can be controlled by an electrical signal. However, the time required for writing data to the digital potentiometer 411 and the time until the resistance value converges to the changed value after that is the time (less than several tens of μs) until the vehicle-mounted device completes transmission after receiving the signal. Satisfaction is the premise.

  Here, the set resistance value is divided with an external resistance as necessary, and is connected to the gain control terminal 4101 of the variable gain power amplifier 410. If it is necessary to correct the temperature characteristics of the entire transmission circuit including the variable gain power amplifier 410, a temperature sensitive element such as a thermistor may be used instead of the voltage dividing resistor.

  With this configuration, the control processing unit 406 switches the resistance value of the digital potentiometer 411 according to the modulation method ASK or QPSK modulation method identified by the modem 405. By switching the resistance value, the output power to be transmitted can be switched through the gain control terminal of the variable gain amplifier 410 for transmission power.

  FIG. 5 is a block diagram showing the configuration of a narrow area communication system radio station according to another embodiment of the present invention. In the figure, the same components as those in FIG. In this embodiment, instead of the digital potentiometer 411 shown in FIG. 4, an analog switch 511 and two voltage dividing resistors 512 and 513 set to appropriate values for both types are used as the analog potentiometer 51. An appropriate transmission output power is obtained by selecting one of the two resistors 512 and 513 in accordance with the ASK / QPSK signal.

  Also in this embodiment, as in the embodiment of FIG. 4, when the modulation system is identified, the gain of the variable gain power amplifier 410 is switched based on the identification result (ASK / QPSK signal). Specifically, if the analog switch 511 is designed to switch to the A side when the modulation method identification result is Hi, and the B side when the modulation method identification result is Lo, the divided voltage set for each can be changed in gain. This can be supplied to the variable gain control terminal 4101 of the power amplifier 410. In the present embodiment as well, it is necessary to take into account the switching time of the analog switch 511 in the same manner as the above-described embodiment. The switching of the analog switch is performed until the vehicle-mounted device performs transmission processing after receiving the signal (within several tens of μs). ). Further, in this embodiment, it is possible to directly switch the variable gain control of the variable gain power amplifier 410 using the identification result in the modem 405 without using the control processing unit 406 of FIG. For example, as shown in FIG. 2, the control processing unit 24 is connected to the high-frequency transmission / reception unit 22, the HMI 25, the IC card 26, the car navigation system 27, and the like. There is a possibility of delay. Therefore, the present embodiment that can realize variable gain switching without using the control processing unit 24 is particularly effective when such a problem occurs.

  With the power amplifier gain switched as described above, it is possible to independently set the transmission output power during ASK modulation transmission and during π / 4 shift QPSK modulation transmission.

  FIG. 6 is a configuration block diagram of a narrow area communication system radio station according to still another embodiment of the present invention. In the figure, the same components as those in FIGS. 4 and 5 are denoted by the same reference numerals, and redundant description is avoided. In this embodiment, as in FIG. 5, instead of the digital potentiometer 411 in FIG. 4, an analog switch 611 and two voltage dividing resistors 612 and 613 set to appropriate values in both systems are used as an analog potentiometer 61. Used. Therefore, as in FIG. 5, appropriate transmission output power can be obtained according to the ASK / QPSK signal.

  Depending on the gain of the power amplifier switched as described above, the transmission output power can be set independently during ASK modulation transmission and during π / 4 shift QPSK modulation transmission.

  The present invention relates to a transmission circuit of a radio station of a DSRC system that employs an ASK modulation system and a π / 4 shift QPSK modulation system, and in particular, a transmission aiming at low cost and miniaturization of the radio station in a form of obtaining sufficient radio performance. Circuit components can be shared. Specifically, according to the present invention, it is possible to set an optimum transmission output level in each modulation method, and it is possible to improve the performance and communication reliability of the radio station without increasing the cost and the circuit scale. It becomes.

Schematic which looked at a mode that the vehicle equipment and roadside machine of the DSRC system by one Example of this invention are performing wireless communication from the vehicle interior. The system block diagram of the onboard equipment of the DSRC system by one Example of this invention. The figure which shows the flow of a process of the DSRC onboard equipment by one Example of this invention. 1 is a configuration block diagram of a narrow area communication system radio station according to an embodiment of the present invention. The block diagram of the configuration of a narrow area communication system radio station according to another embodiment of the present invention. The block diagram of the configuration of a narrow area communication system radio station according to still another embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... DSRC system vehicle equipment, 12 ... Dashboard, 13 ... Car navigation system, 14 ... Roadside machine, 15, 16 ... Transmission / reception radio wave, 21 ... Antenna, 22 ... High frequency transmission / reception part, 23 ... Modem, 24 ... Control processing part, 25 ... HMI (Human Machine Interface), 26 ... IC Card Interface, 27 ... Car Navigation System Interface, 401 ... Antenna, 402 ... Band Pass Filter, 403 ... Transmission / Reception Switch, 404 ... Reception Circuit Block, 405 ... Modem, 406 ... control processing unit, 407 ... quadrature modulator, 408 ... local oscillator, 409 ... upconverter, 410 ... variable gain power amplifier, 411 ... digital potentiometer, 4111 ... digital control circuit, 4112 ... digital resistance voltage divider , 51 Potentiometer, 511 ... analog switches, 512 and 513 ... dividing resistors.

Claims (11)

  Means for switching transmission output power in a narrow area communication system radio station that transmits in two types of modulation schemes of ASK and π / 4 shift QPSK and shares a power amplification circuit for transmission signals of the two types of modulation schemes A narrow area communication system radio station.   Means for switching transmission output power in a narrow area communication system radio station that transmits in two types of modulation schemes of ASK and π / 4 shift QPSK and shares a power amplification circuit for transmission signals of the two types of modulation schemes And a means for selecting the magnitude of the transmission output power by the switching means according to which of the two types of modulation is used for transmission, and a narrow area communication system radio station.   3. The narrow area communication system radio station according to claim 1, wherein the means for switching the magnitude of the transmission output power includes a digital potentiometer that varies a resistance value by an electrical control signal.   3. The narrow area communication system radio station according to claim 1, wherein the means for switching the magnitude of the transmission output power includes an analog switch for electronically switching the switch by an electrical control signal.   5. The variable gain power amplifier according to claim 1, wherein the transmission circuit includes a variable gain power amplifier, and the means for switching the magnitude of the transmission output power includes a means for adjusting a gain of the variable gain power amplifier. A narrow area communication system radio station.   5. The narrow area according to claim 1, wherein a transmission circuit includes an attenuator, and the means for switching the magnitude of the transmission output power includes means for switching the attenuation amount of the attenuator. Communication system radio station.   In a transmission method of a narrow area communication system radio station that transmits in two types of modulation schemes of ASK and π / 4 shift QPSK and shares a power amplification circuit of a transmission signal by the two types of modulation schemes, A step of determining whether to transmit in accordance with the modulation method, a step of determining the magnitude of the transmission output power according to the determination result, and a step of switching the magnitude of the transmission output power according to the determination A transmission method for a narrow-area communication system radio station.   8. The transmission method of a narrow area communication system radio station according to claim 7, wherein the step of switching the magnitude of the transmission output power adjusts a resistance value of a digital potentiometer by an electric control signal.   8. The transmission method of a narrow area communication system radio station according to claim 7, wherein the step of switching the magnitude of the transmission output power electronically switches the analog switch by an electrical control signal.   10. The transmission method for a narrow area communication system radio station according to claim 7, wherein the means for switching the magnitude of the transmission output power adjusts the gain of a variable gain power amplifier in the transmission circuit.   10. The transmission method for a narrow area communication system radio station according to claim 7, wherein the means for switching the magnitude of the transmission output power switches the attenuation amount of an attenuator in a transmission circuit.

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