JP2007281890A - Compound receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To demodulate reception data without performance deterioration even when the modulation system of reception waves is different in a receiver, e.g., an on-vehicle unit of DSRC required to deal with a plurality of modulation systems. <P>SOLUTION: The on-vehicle unit 10 of DSRC, for example, comprises a means for switching a convergence property of variable gain control of an AGC amplifier 24, a transient response property that the control voltage of the AGC amplifier 24 has, is switched to set the convergence property of an output level of the AGC amplifier 24 to an optimal value at all the time, thereby demodulating a π/4 shift QPSK modulation wave and an ASK modulation wave without performance deterioration. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a composite receiver used for radio wave reception using a plurality of modulation schemes. In particular, the present invention relates to a composite receiver that is used in a vehicle-mounted device of a DSRC system that employs two modulation methods, an ASK modulation method and a π / 4 shift QPSK modulation method, and that uses an AGC amplifier in its demodulation circuit.

  In a radio communication system between a mobile station and a base station, when the base station or the mobile station performs radio communication with the counterpart station using a predetermined modulation scheme from among a plurality of predetermined modulation schemes, The demodulation circuit must be able to cope with the predetermined modulation method.

  For example, in a DSRC (Dedicated Short Range Communications) system that performs wireless communication between an onboard device (mobile station) installed in a vehicle and a roadside device (base station) installed on the roadside, As modulation methods for wireless communication signals, ASK (Amplitude shift keying) modulation method and π / 4 shift QPSK (Quadrature Phase Shift Keying) modulation method are used. Therefore, it is necessary for the vehicle-mounted device to determine the modulation method of its own station based on the modulation method of the roadside device that is the counterpart station, and the vehicle-mounted device itself can use any of the wireless communication by the ASK modulation method and the π / 4 shift QPSK modulation method. It is configured to be able to handle signal reception.

  In order to simply configure the demodulator circuit of such a DSRC on-vehicle device, for example, in a signal demodulator described in Japanese Patent Application Laid-Open No. 2005-136620, orthogonal means are used as means for realizing demodulation of an ASK modulation method and a QPSK modulation method. A configuration that can handle the ASK modulation method by acquiring phase information of the QPSK modulation method in the detection circuit and acquiring the amplitude component from each of the in-phase component and the quadrature component output from the quadrature detection circuit is shown. Yes.

  By the way, in a mobile station, it is generally necessary to consider reception level fluctuations due to fading, shadowing, and the like. In particular, in the case of a DSRC in-vehicle device, since the received wave is a burst signal that rises on the order of several μsec, it is necessary to be able to sufficiently cope with fluctuations in the received level. Therefore, in the DSRC in-vehicle device, the followability to the level fluctuation of the received wave is required for the convergence characteristic of the AGC (Automatic Gain Control) amplifier provided in the receiving circuit.

  For example, if the convergence characteristic of the variable gain control of the AGC amplifier is long in the demodulation of the π / 4 shift QPSK modulation method, the followability with respect to fluctuations in the reception level is deteriorated. In the DSRC system, the burst signal rises on the order of several μsec as described above. Therefore, in order to receive such a burst signal having a fast rise, it is desirable that the convergence characteristics of the AGC amplifier be on the order of several μsec or less in consideration of the burst rise time.

  On the other hand, in the case of the ASK modulation method, the ASK signal has a modulation speed of 2.048 Mbaud. Therefore, in the demodulation of the ASK modulated wave method, in order to extract the amplitude component of the ASK modulated wave from the output of the AGC amplifier, the amplitude of the ASK modulated wave is thus changed at a modulation speed of 2.048 Mbaud. The convergence characteristic of the variable gain control of the AGC amplifier is desired to be sufficiently slow with respect to the modulation speed. This is because when the convergence characteristic of AGC is fast with respect to the modulation speed (2.048 Mbaud) of the ASK modulation method, the AGC loop functions to absorb the amplitude information of the ASK modulation wave, and the AGC amplifier This is because the amplitude information of the ASK modulated wave may be lost from the output.

  In this way, it is essential to consider the convergence characteristics of AGC in order to use either the π / 4 shift QPSK modulation method or the ASK modulation method using an AGC amplifier in the receiving circuit of the DSRC on-board unit. Absent.

  However, in the signal demodulator described in Japanese Patent Application Laid-Open No. 2005-136620, the convergence characteristics of the variable gain control of the AGC amplifier are as follows: when receiving a wireless communication signal of π / 4 shift QPSK modulation method and when using a wireless signal of ASK modulation method. No consideration has been given to receiving communication signals.

JP 2005-136620 A

  As described above, in a composite receiver that needs to support a plurality of modulation schemes, for example, a DSRC on-vehicle device, the modulation scheme of the received wave includes an ASK modulation scheme in which information is included in the amplitude component, and information in the phase component. Since there is a mounted π / 4 shift QPSK modulation method, it is necessary to support both modulation methods. For this purpose, the DSRC in-vehicle device uses an AGC amplifier that performs variable gain control so that the output amplitude level becomes constant, and extracts phase information from the output in the case of π / 4 shift QPSK demodulation to perform ASK demodulation. In some cases, a configuration for extracting amplitude information is employed.

  However, in order to support both the π / 4 shift QPSK modulation method and the ASK modulation method in the DSRC in-vehicle device, as described above, the optimum variable gain control of the AGC amplifier corresponding to each modulation method. Have different convergence characteristics. That is, when receiving a π / 4 shift QPSK modulated wave, it is desirable that the convergence characteristic of the variable gain control of the AGC amplifier is fast in consideration of the transient response characteristic of the burst signal specified by the DSRC system. When receiving the modulated wave, it is desirable that the convergence characteristic of the variable gain control of the AGC amplifier is sufficiently slow with respect to the modulation speed of the ASK modulation method defined by the DSRC system.

  As a result, in the DSRC in-vehicle device, the convergence characteristics of the optimum variable gain control of the AGC amplifier are different from each other according to the difference in the modulation method, and the π / 4 shift QPSK modulated wave and the ASK modulated wave are received. In some cases, it is difficult to achieve both reception performance (demodulation performance).

  The present invention has been made to solve the above-described problems, and relates to a composite receiver used for receiving a radio wave using a plurality of modulation methods, and an AGC amplifier provided in the receiving circuit thereof. An object of the present invention is to provide a composite receiver that improves the demodulation performance by providing means for switching the convergence characteristics of the variable gain control according to the modulation method of the received signal.

  In order to solve the above problem, a receiver that needs to support a plurality of modulation schemes, for example, a DSRC in-vehicle device, is provided with means for switching the convergence characteristic of the variable gain control of the AGC amplifier. By setting the optimum value, demodulation of the π / 4 shift QPSK modulated wave and the ASK modulated wave can be performed without deterioration in performance.

  Specifically, the transient response characteristic of the control voltage for performing AGC control is switched. For example, the above-mentioned problem is solved by switching the time constant of a low-pass filter configured in an analog manner such as a resistor and a capacitor, or a digital filter configured logically.

  According to the present invention, a receiver that needs to support a plurality of modulation schemes, for example, a demodulator circuit of a DSRC on-board unit that needs to support both a π / 4 shift QPSK modulation scheme and an ASK modulation scheme, is provided with an AGC amplifier. In this case, the modulation characteristic of the AGC amplifier is switched to the optimum value in each modulation method, so that demodulation processing can be performed without performance degradation in both modulation methods.

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

  The embodiment of the composite receiver of the present invention is illustrated in the drawings, taking as an example the case of application to a vehicle-mounted device in a DSRC system in which a vehicle-mounted device mounted on a vehicle and a roadside device installed on the roadside perform wireless communication. This will be explained based on this.

  FIG. 1 is a configuration diagram of a DSRC system to which a composite receiver according to an embodiment of the present invention is applied as a vehicle-mounted device, and shows a state in which the vehicle-mounted device of the DSRC system and a roadside device are performing wireless communication. It is.

  In FIG. 1, reference numeral 10 denotes an on-vehicle device as a composite receiver. In the illustrated example, an antenna 11 used for communication with a roadside device 50 described later is integrated with a main body housing 10 </ b> A of the on-vehicle device 10. It has become. For this reason, in the illustrated example, a state in which the main body housing 10A of the vehicle-mounted device 10 is installed on the dashboard 91 in the vehicle compartment so as to easily transmit and receive radio signals is shown. In the case of the vehicle-mounted device 10 in which the main body housing 10A of the vehicle-mounted device 10 and the antenna 11 are separated, only the antenna 11 may be installed on a dashboard 91 in a place where radio signals can be easily transmitted and received. In this case, there is no restriction on the installation location of the main body casing 10A of the vehicle-mounted device 10.

  On the other hand, 50 is a roadside machine, for example, provided on the roadside such as a toll gate on a toll road or a parking lot entrance / exit, and performs two-way communication with the vehicle-mounted device 10 by DSRC to settle the toll and parking fee. Various information service processing including processing and road information is performed. Therefore, the roadside device 50 is provided with a roadside antenna 51 for performing wireless communication with the vehicle-mounted device 10 of the passing vehicle toward the vehicle passing through the installation place. When the vehicle enters the communication area created by the roadside antenna 51, the roadside machine 50 starts communication with the vehicle-mounted device 10 provided in the approaching vehicle, and the vehicle is within the communication area. Two-way communication with the in-vehicle device 10 becomes possible.

  Each of the roadside devices 50 is connected to the vehicle-mounted device 10 of the vehicle that has entered the communication area, with a predetermined modulation method, specifically, an ASK modulation method in which information is placed on an amplitude component or a phase component. The radio signal radio wave is transmitted / received by any one of the π / 4 shift QPSK modulation schemes in which information is placed on, and information communication is performed.

  FIG. 2 is a system block diagram of the vehicle-mounted device as the composite receiver according to the embodiment of the present invention.

  In the present embodiment, the vehicle-mounted device 10 includes an antenna 11, a transmission / reception unit 12, a control / processing unit 13, an HMI (human machine interface) unit 14, an operation unit 15, a SAM (security module) unit 16, and a storage device unit. 17 is provided.

  The transmission / reception unit 12 includes a transmission circuit 12t and a reception circuit 12r. A radio signal based on DSRC transmitted from the roadside device 50 by either the ASK modulation method or the π / 4 shift QPSK modulation method is transmitted to the antenna 11 Is received by the receiving circuit 12r. The receiving circuit 12r demodulates the received data signal included in this received signal. The demodulated received data signal is supplied from the transmission / reception unit 12 to the control / processing unit 13. Further, the transmission / reception unit 12 converts the transmission data signal supplied from the control / processing unit 13 according to either the ASK modulation method or the π / 4 shift QPSK modulation method of the radio signal previously received from the roadside device 50. Modulation is performed by the transmission circuit 12t to generate a transmission signal, which is wirelessly output via the antenna 11.

  The control / processing unit 13 performs, for example, a reception process of received data from the roadside device 50 supplied from the transmission / reception unit 12 for the various information service processes described above according to a user instruction supplied from the HMI unit 14 or the like. Data processing such as generation processing of transmission data wirelessly transmitted to the roadside device 50 via the transmission / reception unit 12 and data reading / writing processing with the storage device unit 17 are performed, and the above-described units of the vehicle-mounted device 10 are operated. Control.

  The HMI unit 14 controls the supply of a user instruction based on a predetermined operation of the operation unit 15 to the control / processing unit 13 and operates a notification signal based on the processing result of the control / processing unit 13 with the operation unit 15. And supply control to the unit 15.

  The SAM unit 16 encrypts the write data and decrypts the read data when the control / processing unit 13 performs a data read / write process with the storage device unit 17.

  In the illustrated example, the storage device unit 17 includes an IC card 18 as a portable storage medium and an IC card read / write device 19 that reads / writes data from / to the IC card.

  In the case of the illustrated embodiment, the in-vehicle device 10 includes an interface 20 that can perform mutual communication with the car navigation system 60 that is also provided in the vehicle, and is attached to the control / processing unit 13. In order to improve usability by outputting the information of the above, instructing the vehicle-mounted device 10 or inputting the information, etc., each other can be linked.

  Next, the configuration of the reception circuit 12r of the transmission / reception unit 12 in the vehicle-mounted device 10 as the composite receiver described above will be described with reference to FIG.

FIG. 3 is a circuit block diagram of an embodiment of a receiving circuit in the transmission / reception unit of the vehicle-mounted device.
The reception circuit 12r in the transmission / reception unit 12 uses an AGC amplifier 24, and has a circuit configuration corresponding to demodulation of two modulation schemes of a π / 4 shift QPSK modulated wave and an ASK modulated wave.

  In FIG. 3, the reception circuit 12r includes a frequency down converter 21, a local oscillator 22, a band pass filter 23, an AGC amplifier 24, an orthogonal demodulation circuit 25, a low pass filter 29, an AD converter 30, and a π / 4 shift QPSK demodulation. A block 31, a detector 32, an ASK demodulation block 33, an AGC control calculation unit 34, and a low-pass filter 35 are provided.

  The received signal received by the antenna 11 shown in FIG. 2 is amplified to an amplitude suitable for subsequent processing by an amplifier (not shown), and this amplified received signal is input to the frequency down converter 21. In the frequency down converter 21, the input received signal is mixed with the local oscillation signal output from the local oscillator 22 and frequency-converted to an intermediate frequency signal. The reception signal frequency-converted to the intermediate frequency signal is input to the band pass filter 23, and a signal in a desired frequency band is extracted.

  The AGC amplifier 24 is an amplifier that tries to keep the output level constant by an external control signal even when the input signal level changes. In the on-vehicle device 10 shown in the figure, the input received signal level, that is, the received signal level extracted by the band pass filter 23 is determined based on the distance from the roadside device 50 to the on-vehicle device 10, and further the ASK modulation method or π / 4. Even when the shift QPSK modulation method changes due to the difference in the modulation method on the transmission side, the AGC amplifier 24 variably controls the gain based on the control signal from the outside so as to keep the output signal level constant. To do.

  The quadrature demodulation circuit 25 includes two multipliers 26 and 26, an oscillator 27, and a π / 2 phase shifter 28, and reception via the AGC amplifier 24 is provided on the input side of each multiplier 26 and 26. The signal is branched and connected. In the quadrature demodulation circuit 25, one multiplier 26 multiplies the received signal by the output of the oscillator 27, and the other multiplier 26 multiplies the received signal by the output obtained by shifting the output of the oscillator 27 by the π / 2 phase shifter 28. Then, the received signal is orthogonally detected.

  The low-pass filters 29 and 29 are connected to the multiplication outputs (demodulation outputs) of the orthogonal demodulation circuit 25, respectively, and remove the respective high-frequency components (high-frequency components). ADCs (Analog Digital Converters) 30 and 30 A / D convert the outputs of the low-pass filters 29 and 29 to demodulate the in-phase component digital output I and the quadrature component digital output Q, respectively.

  The π / 4 shift QPSK demodulation block 31 obtains phase information from the in-phase component digital output I and the quadrature component digital output Q, and delay-detects this to obtain QPSK demodulated data. The π / 4 shift QPSK demodulation block 31 supplies the demodulated QPSK demodulated data to the control / processing unit 13.

  The detector 32 is connected to the output side of the AGC amplifier 24 together with the input terminal of the quadrature demodulation circuit 25. For example, the received signal that has passed through the AGC amplifier 24 is subjected to quadrature detection, and the in-phase component digital output I obtained thereby is detected. And the quadrature component digital output Q are calculated and reproduced as an amplitude signal (amplitude information).

  The ASK demodulation block 33 compares the obtained amplitude signal with a threshold value and binarizes it to obtain ASK demodulated data. The ASK demodulation block 33 supplies the demodulated ASK demodulated data to the control / processing unit 13.

  The AGC control calculation unit 34 receives an amplitude signal obtained by averaging the in-phase component digital output I and the quadrature component digital output Q from the detector 32, and, for example, a predetermined amplitude reference value of the amplitude value of the amplitude signal. And a control voltage for controlling the gain of the AGC amplifier 24 is generated based on the error.

  In the case of the present embodiment, the low-pass filter 35 can switch its transient response characteristic in accordance with a control signal supplied from the control / processing unit 13.

  Next, the operation of the DSRC vehicle-mounted device 10 of the present embodiment configured as described above will be described.

FIG. 4 is a diagram showing a flow of reception processing of the DSRC on-vehicle device 10 according to the present embodiment.
First, when the vehicle-mounted device 10 detects that it has entered the communication zone of the roadside device 50 shown in FIG. 1 (step S10), the received wave from the roadside device 50 at that time (that is, transmission transmitted by the roadside device 50) The modulation method used for communication with the roadside device 50 is identified according to the wave (step S20). In the case of the present embodiment, the specific identification of this modulation method is performed by controlling / processing the QPSK demodulated data supplied from the π / 4 shift QPSK demodulating block 31 and the ASK demodulated data supplied from the ASK demodulating block 33. This is performed by the control / processing unit 13 through data processing by the unit 13. Therefore, in the case of the DSRC in-vehicle device 10 according to the present embodiment, it is necessary to assume reception of the above-mentioned two modulation schemes when entering the communication zone of the received wave from the roadside device 50, that is, demodulation of the above-mentioned two modulation schemes. It has a configuration with both circuits.

  Next, when the control / processing unit 13 identifies the modulation method of the received wave from the roadside device 50 as described above, the on-vehicle device 10 determines the transient response characteristics of the low-pass filter 35 according to the identification result. Control as follows.

  For example, when receiving the transmission signal from the roadside device 50 modulated by the π / 4 shift QPSK modulation method, the in-vehicle device 10 receives the quadrature demodulation circuit 25, the low-pass filters 29, 29 from the output of the AGC amplifier 24. , And ADC converters 30 and 30 demodulate the in-phase component digital output I and the quadrature component digital output Q, and the π / 4 shift QPSK demodulation block 31 obtains phase information from the in-phase component digital output I and the quadrature component digital output Q. In order to demodulate the received wave that rises in a burst as the roadside unit 50 enters the communication zone, the AGC amplifier 24 takes into account fluctuations in the amplitude level that occur when the received wave rises in bursts. Must have convergence properties.

  For example, assuming that the erasure preamble period allowed in the demodulating circuits 25, 29, 30, and 31 at the subsequent stage of the AGC amplifier 24 is 3 μs from the rising edge of the received wave, the AGC amplifier 24 is within 3 μs. It must be converged.

FIG. 5 is a diagram showing an example of the convergence characteristics of the output level of the AGC amplifier.
The example shown in FIG. 5 shows the transition of the output level of the AGC amplifier 24 when the reception level of the received signal received via the antenna 11 in the vehicle-mounted device 10 fluctuates. An example in which the output level converges at 3 μs is shown.

  However, contrary to the example shown in FIG. 5, when the convergence time of the output level of the AGC amplifier 24 exceeds the allowable preamble period (3 μs), the output level of the AGC amplifier 24 converges. Since the received bits of the QPSK demodulated data are lost in the π / 4 shift QPSK demodulating block 31 only for the time up to this time, data synchronization is performed in the demodulator circuit (for example, the control / processing unit 13). A reception error occurs.

  Therefore, when receiving a transmission signal from the roadside device 50 modulated by the π / 4 shift QPSK modulation method, the output of the AGC amplifier 24 is taken into account in consideration of the erasure preamble period that occurs at the rising edge of the burst of the received wave. It is desirable that the level converges within a short period (erasure preamble period).

  On the other hand, when receiving a transmission signal from the roadside device 50 modulated by the ASK modulation method, an amplitude signal (amplitude information) is extracted from the output of the AGC amplifier 24 by the detector 32. In this case, the AGC amplifier The convergence time of 24 is preferably long. Specifically, it is desirable that the convergence time is sufficiently long with respect to the symbol width of the ASK modulated wave defined as a modulation rate of 2.048 Mbaud in DSRC.

FIG. 6 is a diagram illustrating an example of convergence characteristics of the output level of the AGC amplifier and an output example of the detector at that time.
The example shown in FIG. 6 shows the output waveform of the AGC amplifier 24 and the output waveform of the detector 32 when the convergence time of the output level of the AGC amplifier 24 is sufficiently longer than the symbol width of the ASK modulated wave. It is.

  As described above, when the convergence time of the AGC amplifier 24 is sufficiently longer than the symbol width of the ASK modulated wave, the amplitude component (amplitude information) from the detector 32 is not lost without the amplitude component of the ASK modulated wave being lost. ) Is output. Note that the level fluctuation of the received wave that rises in bursts at the time of entering the communication zone of the received wave from the roadside device 50 does not cause a problem in this method.

FIG. 7 is a configuration diagram of an ASK demodulation circuit as an embodiment of the ASK demodulation block shown in FIG.
The ASK demodulating circuit 33 according to this embodiment is configured to include a comparison circuit 331 and a low-pass filter (LPF) 332, and the output of the detector 32 is directly input to the non-inverting input (+ input) of the comparison circuit 331. The reference input (−input) is input via the low-pass filter 332. In this case, by appropriately selecting the low-pass filter 332, burst fluctuations in the reception level can be absorbed, and the ASK amplitude component can be extracted by the comparison circuit 331.

  However, contrary to the example shown in FIG. 6, when the convergence time of the output level of the AGC amplifier 24 is shorter than the symbol width of the ASK modulated wave, the output of the AGC amplifier 24 uses the amplitude information of the ASK modulated wave. Since AGC works so as to absorb, amplitude information cannot be extracted from the output of the AGC amplifier 24.

  For this reason, when receiving the transmission signal from the roadside device 50 modulated by the ASK modulation method, it is desirable that the convergence time of the output level of the AGC amplifier 24 is sufficiently longer than the symbol width of the ASK modulated wave.

  Therefore, in the vehicle-mounted device 10 according to the present embodiment, the AGC amplifier is switched by switching the transient response characteristics of the control voltage applied to the control terminal of the AGC amplifier 24 according to the identification result of the modulation method of the received wave from the roadside device 50. The convergence time of 24 output levels is switched to optimize reception according to the difference in the received wave modulation method.

FIG. 8 is a block diagram of an embodiment of the low-pass filter shown in FIG.
In the example shown in FIG. 8, the low-pass filter 35 is connected in parallel to a resistor R having one side connected to the AGC control calculation unit 34 and the other side connected to the control terminal of the AGC amplifier 24. A transient response circuit is provided that includes capacitors C1 and C2 that are connected and connect the other side of the resistor R to the ground. A switch SW is connected in series to one of the capacitors C1 and C2 so that the other side of the resistor R can be connected to and disconnected from the ground. In this case, the opening / closing of the switch SW is controlled based on the control signal supplied from the control / processing unit 13 according to the identification result of the modulation method of the received wave from the roadside device 50 described above. ing.

  Here, the time constant of the transient response characteristic of the low-pass filter as shown in FIG. 8 is obtained by the product R · C [s (second)] of the resistor R and the capacitor C, but the low-pass filter shown in FIG. In the case of the filter 35, the time constant of the low-pass filter 35 is switched by performing control so that the capacitor C2 is added in parallel to the capacitor C1 according to the opening and closing of the switch SW. Yes.

  That is, when the switch SW is off (open), the time constant of the low-pass filter 35 is R1 · C [s], whereas when the switch SW is on, the time constant of the low-pass filter 35 is R · (C1 + C2) [s]. Therefore, the control / processing unit 13 turns off the switch SW when the received wave modulation method is π / 4 shift QPSK modulation and switches SW when the received wave modulation method is ASK modulation according to the identification result of the received wave modulation method from the roadside device 50. The time constant of the low-pass filter 35 is switched so as to be turned on.

  As a result, when the modulation method of the received wave is π / 4 shift QPSK modulation, the AGC amplifier 24 is converged within the erasure preamble period generated at the rising edge of the received wave burst, and during the ASK modulation, the AGC amplifier 24 is It is converged in a sufficiently long time with respect to the symbol width of the modulated wave.

  The vehicle-mounted device 10 according to the present embodiment is intended to switch the convergence time of the AGC amplifier 24, and the specific configuration and specific method are not limited to the above-described configuration and method.

  Further, regarding the method for identifying the modulation method of the received wave from the roadside device 50, the specific method is not limited to the above-described method.

  For example, if the convergence time of the output level of the AGC amplifier 24 is set to be long as an initial state, it is advantageous for demodulating the received wave by the ASK modulation method as described above, but reception by the π / 4 shift QPSK modulation method. It is vulnerable to sudden reception level fluctuations such as burst rising at the time of wave demodulation. However, since the modulation scheme is identified when entering the communication zone, the reception level at that time is very weak. For this reason, the amplitude level of the received wave that rises in a burst manner is not significantly different from the reception level at the time of no signal, and strict specifications regarding the AGC convergence time are not required.

  Conversely, if the convergence time of the output level of the AGC amplifier 24 is set short as an initial state, it is disadvantageous for demodulation of the received wave by the ASK modulation system as described above, but π / 4 shift QPSK modulation. This is advantageous for demodulating the received wave by the method. As a method for identifying the modulation method in this case, attention should be paid to the phase component of the received wave received from the roadside device 50, for example. That is, in the case of ASK modulation, the phase component does not change, but in the case of π / 4 shift QPSK modulation, the phase component fluctuates. Therefore, it is only necessary to identify the modulation method using this characteristic, and ASK demodulation cannot be performed. However, the modulation scheme can be identified.

  As described above, regarding the method for identifying the modulation method, it is sufficient that the modulation method can be identified before the start of communication, and the method is not limited to the above.

  Next, another embodiment of the receiving circuit 12r in the transmitting / receiving unit 12 of the vehicle-mounted device 10 will be described with reference to the drawings. In the description of the configuration, the same or similar components as those in the embodiment of the receiving circuit 12r shown in FIG. 3 are denoted by the same reference numerals in the drawing, and the detailed description thereof is omitted.

FIG. 9 is a circuit block diagram of an embodiment of a receiving circuit in the transmission / reception unit of the vehicle-mounted device.
In the case of the receiving circuit 12r of the present embodiment, the configuration up to the output of the AGC amplifier 24 is the same as that of the receiving circuit 12r shown in FIG. 3, but the control voltages of the level detecting means 41 and the AGC amplifier 24 for detecting the receiving level are set. The digital filter 42 to be controlled and the processing means of the control / processing unit 13 for determining the time constant of the convergence characteristic of the AGC control voltage are different from the configuration of the receiving circuit 12r shown in FIG.

  First, in this embodiment, the output of the AGC amplifier 24 is divided into an in-phase component digital output I and a quadrature component digital output Q by the quadrature demodulation circuit 25. The in-phase component digital output I and the quadrature component digital output Q are captured by the ADCs 30 and 30 and used for digital processing such as π / 4 shift QPSK demodulation by the π / 4 shift QPSK demodulation block 31 in the subsequent stage. The means 41 detects the reception level from the in-phase component digital output I and the quadrature component digital output Q. Specifically, the received electric field strength can be relatively known by obtaining the square root of the sum of the squares of the in-phase component digital output I and the quadrature component digital output Q.

  Based on the reception level thus obtained, the AGC control calculation unit 34 causes the digital filter 42 to generate an AGC control voltage of the AGC amplifier 24. In this case, it is assumed that the time constant of the transient response characteristic of the AGC control voltage can be controlled by this logically configured digital filter 42. That is, by switching the digital output of the digital filter 42, the convergence characteristics of the AGC control voltage are switched according to the two modulation schemes defined by the DSRC. In this case, there is no need to add external components such as a filter configured in an analog manner.

  Even in the case of the present embodiment zero, the same effect as in the above-described embodiment can be achieved by performing the variable gain control of the AGC amplifier by the AGC control voltage.

  As described above, also in the case of the present embodiment, by switching and using the convergence characteristics of the output level of the AGC amplifier 24, the ASK modulation wave defined by DSRC and the demodulation of the π / 4 shift QPSK modulation wave are obtained. This can be done without adding a large-scale circuit and processing. Further, the level detection means 41 for detecting the reception level, the digital filter 42 for controlling the control voltage of the AGC amplifier 24, and the combination thereof are not limited to the above embodiment.

  The present invention relates to a demodulation method in wireless communication using a plurality of modulation schemes. In particular, in a demodulator circuit of a vehicle-mounted device of a DSRC system in which the demodulator circuit needs to support the above-described two modulation schemes, when the demodulator circuit is configured using an AGC amplifier, reception level fluctuations during π / 4 shift QPSK modulation occur. This makes it possible to satisfy both the following capability and the demodulation performance during ASK modulation.

1 is a configuration diagram of a DSRC system to which a composite receiver according to an embodiment of the present invention is applied as a vehicle-mounted device. It is a system block diagram of the onboard equipment as a composite receiver by one embodiment of this invention. It is a circuit block diagram of one Example of the receiving circuit in a transmission / reception part. It is a figure which shows the flow of a reception process of the DSRC onboard equipment by this Embodiment. It is the figure which showed an example of the convergence characteristic of the output level of AGC amplifier. It is the figure which showed an example of the convergence characteristic of the output level of AGC amplifier, and the output example of the detector in that case. It is a block diagram of the ASK demodulation circuit as one Example of the ASK demodulation block shown in FIG. It is a block diagram of one Example of the low-pass filter shown in FIG. It is a circuit block diagram of one Example of the receiving circuit in the transmission / reception part of onboard equipment.

Explanation of symbols

10 Onboard equipment (composite receiver)
10A Main Body 11 Antenna 12 Transmitter / Receiver 12r Receiver 12t Transmitter 13 Control / Processing Unit 14 HMI (Human Machine Interface) 15 Operation Unit 16 SAM (Security Module) 17 Storage Device 21 Frequency Down Converter 22 Local Oscillator 23 Band pass filter 24 AGC amplifier 25 Quadrature demodulation circuit 26 Multiplier 27 Oscillator 28 π / 2 phase shifter 29 Low pass filter 30 AD converter 31 π / 4 shift QPSK demodulator block 32 Detector 33 ASK demodulator block 34 AGC control calculation unit 35 Low-pass filter 41 Level detection means 42 Digital filter 50 Roadside device 60 Car navigation system

Claims (4)

A composite receiver capable of demodulating a plurality of modulation methods,
A power amplifier capable of variably controlling the gain so as to obtain a constant amplitude level output;
And a means for switching the convergence characteristics of the gain control of the power amplifier in accordance with the modulation method of the received wave. The composite receiver according to claim 1,
A composite receiver comprising means for identifying a modulation method of a received wave. The composite receiver according to claim 2,
One of the plurality of modulated waves is an amplitude modulation method,
A composite receiver comprising means for intentionally setting a convergence characteristic of variable gain control of the power amplifier when receiving the amplitude-modulated wave. The composite receiver according to claim 2,
The plurality of modulated waves are a π / 4 shift QPSK modulation method and an ASK modulation method,
In the two modulation schemes, the variable gain control of the power amplifier is such that the convergence characteristic is fast when receiving a π / 4 shift QPSK modulated wave, and the convergence characteristic is slow when receiving an ASK modulated wave. And a means for switching the convergence characteristic.

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