JP2012193514A - Communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve security of a communication system.SOLUTION: The phases of both phase signals are set to be mutually different. Herein, the unlock of a vehicle door may be executed by using a relay to establish an improper communication between an on-vehicle device 20 and an electronic key 10 located far away from each other. When relaying LF-band radio signals, the relay detects the received radio signals once and, based on its detected signals, creates and transmits radio signals having higher-intensity radio waves. In this case, the phases of both phase signals, which are mutually different, become the same phase during envelope detection of the received radio signals (the phase signals). Thus, when using the relay for the improper communication, the determination that the phases of both phase signals are not different is made to restrict the unlock of the vehicle door.

Description

  The present invention relates to a communication system.

  2. Description of the Related Art Conventionally, in an electronic key system that is a type of communication system, locking and unlocking of a vehicle door, engine starting, and the like are permitted through wireless communication between the electronic key and the vehicle. For example, the vehicle transmits a request signal inside and outside the vehicle. When receiving the request signal, the electronic key transmits a response signal including an ID code. When verification of the ID code included in the response signal is established, the vehicle permits locking / unlocking of the vehicle door and starting of the engine (see, for example, Patent Document 1).

JP 2007-170162 A

  In recent years, there has been concern about unauthorized communication in which an electronic key that exists far away using a relay device that relays radio waves (request signal and response signal) is disguised as if it exists around the vehicle. Unauthorized communication using this repeater may cause unlocking of the vehicle door and the like. Therefore, security measures against unauthorized communication using a repeater are required.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a communication system with improved security.

Hereinafter, means for achieving the above-described object and its operation and effects will be described.
The invention according to claim 1 is a communication system that permits control of a controlled object through transmission / reception of a radio signal between a first communication device and a second communication device, at least one of which is a mobile communication device, The wireless signal is time-divisionally transmitted from the first communication device or simultaneously as a LF-band wireless signal under a specific phase condition, and the signal received by the second communication device is the specific phase condition. When it is determined that the communication is not permitted, the execution of the control is permitted as it is not an unauthorized communication using the repeater. When it is determined that the specific phase condition is not satisfied, the control The gist is to prohibit execution.

  According to this configuration, a radio signal is transmitted in a time division manner or simultaneously with a specific phase condition. Here, even if both communication devices are located far away, control can be performed by establishing communication illegally using a repeater that relays the radio signal from the first communication device to the second communication device. May be executed. Generally, when relaying an LF band radio signal, the repeater detects the received radio signal once and transmits a radio signal having a stronger radio wave based on the detected signal. Here, when the received radio signals are detected (envelope detection), the phases different in these signals become the same phase. For this reason, in the case of unauthorized communication using a repeater, it is determined that a specific phase condition in the radio signal is not satisfied, and execution of control is prohibited. Thereby, security can be improved.

  According to a second aspect of the present invention, in the communication system according to the first aspect, the specific phase condition is a phase difference between the first signal and the second signal transmitted in a time division manner as the radio signal. The first or second communication device includes a process determination unit, and the process determination unit receives a phase of the received first or second signal when the received signal exceeds a certain level. Comparison between the reproduction unit to reproduce, the phase comparison unit that compares the phase of the signal reproduced by the reproduction unit with the phase of the first or second signal currently received, and the comparison result of the phase comparison unit A phase difference determination unit that determines whether or not a phase difference has occurred between the currently received signal and the timing at which the signal being received is switched from the first signal to the second signal. It is expected that a phase difference will be detected by the phase difference determination unit. A signal processing unit for recognizing time to be detected, and when determining that a phase difference has occurred through the phase difference determination unit at a time when the phase difference recognized through the signal processing unit is expected to occur, The execution of the control is permitted as not being an unauthorized communication used, and when it is determined that no phase difference has occurred through the phase difference determination unit at a time when the phase difference is expected to occur, an illegal operation using a repeater is performed. The gist is to prohibit the execution of the control as communication.

  The reproduction unit starts reproduction of the phase when the input signal is received at a certain level or more, and immediately after the input signal is switched from the first signal to the second signal, the reproduction unit reproduces the phase of the first signal. Therefore, immediately after switching from the first signal to the second signal, two signals having different phases are input to the phase comparison unit. The phase difference determination unit determines the phase difference based on the comparison result of the phase comparison unit. On the other hand, the signal processing unit recognizes the time when the phase difference is expected to be detected. This time is set immediately after switching between both signals. As a result, when the communication is not unauthorized using the repeater, it is determined that the phase difference has occurred between the two signals through the phase difference determination unit at the time when the phase difference is expected to occur. When this determination is made, execution of control is permitted. In addition, in the case of unauthorized communication using a repeater, execution of control is prohibited by determining that there is no phase difference between the two signals through the phase difference determination unit at a time when a phase difference is expected to occur. Is done. Thereby, security can be improved.

  According to a third aspect of the present invention, in the communication system according to the second aspect, the first communication device includes the processing determination unit and is provided in the vehicle that is the control target. The communication device is provided as an electronic key possessed by the user. When the electronic key receives the first and second signals in the LF band transmitted from the first communication device, the UHF band corresponding to the signal is received. The first communication device transmits the first and second signals to the first communication device, and the first communication device detects the received first and second signals in the UHF band, thereby obtaining the signals. The gist is to have the same phase as the first and second signals in the LF band.

According to this configuration, an electronic key that requires higher portability can be configured in a compact manner by providing a processing determination unit in the vehicle.
According to a fourth aspect of the present invention, in the communication system according to the second or third aspect, a control request signal for requesting control as the radio signal is transmitted between the two communication devices. The gist of the second signal is that it is transmitted as a phase signal separately from the control request signal.

  According to this configuration, the first and second signals are transmitted as phase signals separately from the control request signal. Accordingly, the control request signal and the phase signal can be transmitted in different directions between the two communication devices.

  According to a fifth aspect of the present invention, in the communication system according to the first aspect, the specific phase condition is a phase difference between the first signal and the second signal transmitted simultaneously as the radio signal. That is, when the second communication device determines that there is a phase difference between the two signals based on the signal strength of the signal in which the two signals interfere with each other, the second communication device determines that the specific phase condition is satisfied. Is the gist.

  According to this configuration, even when the first and second signals are transmitted simultaneously, it is possible to determine whether there is a phase difference between the signals. This is because, for example, when both signals are in opposite phases, interference occurs and the signal intensity is reduced, and when both signals are in phase, the signal intensity is increased. Thereby, the time required for transmitting the first and second signals can be shortened.

  According to the present invention, security can be improved in a communication system.

The block diagram of the electronic key system in 1st Embodiment. The block diagram of the LF transmission part in the vehicle in 1st Embodiment. (A) in the first embodiment is a graph showing a reference signal, (b) is a graph showing transmission signals from the first and second transmission antennas, and (c) is a graph showing an on / off state of the switch. . The timing chart which showed the transmission timing of the various signals in 1st Embodiment. The block diagram of the process determination part etc. in 1st Embodiment. The graph which showed the signal waveform-shaped by the waveform shaping part in 1st Embodiment. (A) in the first embodiment is a graph showing a signal from the clock recovery unit, (b) is a graph showing a signal from the waveform shaping unit, and (c) is a graph showing a signal from the phase comparison unit. . The graph which showed the fixed time when the phase difference in 1st Embodiment is detected. The block diagram of the electronic key system in 2nd Embodiment. (A) is a graph showing the signal from the amplifier, (b) is a graph showing the signal from the diode, (c) is a graph showing the signal output to the amplifier, and (d) is a signal from the envelope detector. Graph showing.

(First embodiment)
Hereinafter, a first embodiment of an electronic key system according to the present invention will be described with reference to FIGS.

As shown in FIG. 1, the electronic key system 1 includes an electronic key 10 possessed by a user and an in-vehicle device 20. Mutual communication is performed between the electronic key 10 and the in-vehicle device 20, and the locking and unlocking of the vehicle door is permitted on the condition that the mutual communication is established. Hereinafter, the configuration of the electronic key system will be described.
<In-vehicle device>
As shown in FIG. 1, the in-vehicle device 20 includes an in-vehicle control unit 21, an LF transmission unit 22, a first transmission antenna 22a, a second transmission antenna 22b, a UHF reception unit 24, and a reception antenna 24a. It is equipped with. In addition, a lock switch 31 and a door lock device 32 are electrically connected to the in-vehicle control unit 21.

  Both transmitting antennas 22a and 22b are built in the outside door handle of the vehicle door. The lock switch 31 is provided on the surface of the outside door handle, and outputs an operation signal to that effect to the in-vehicle control unit 21 when pressed by the user. The UHF receiver 24 is provided in the approximate center of the vehicle interior. The door lock device 32 automatically locks and unlocks the vehicle door when the vehicle door is closed.

  The in-vehicle control unit 21 is configured by a computer unit and includes a nonvolatile memory 21a. In the memory 21a, the same ID code as the ID code stored in the electronic key 10 is stored.

As shown in FIG. 2, the LF transmission unit 22 includes a reference oscillator 41, a phase shifter 42, a modulator 43, and switches 44a and 44b.
The reference oscillator 41 is connected to the transmission antenna 22a via the switch 44a and to the transmission antenna 22b via the phase shifter 42 and the switch 44b. The modulator 43 is connected to each of the switches 44a and 44b and switches them on and off.

  As shown in FIG. 3A, the reference oscillator 41 generates a reference signal of an LF (Low Frequency) band (for example, 125 kHz) and outputs it to the antennas 22a and 22b. As shown in FIG. 3C, the modulator 43 turns on and off the switches 44 a and 44 b according to the digital signal from the in-vehicle control unit 21. The digital signal is composed of “0” and “1”, for example. When receiving “0”, the modulator 43 turns off one of the switches 44a and 44b, and turns on one of the switches 44a and 44b when receiving “1”. As a result, as shown in FIG. 3B, a transmission signal whose amplitude is changed according to “0” and “1” of the digital signal is generated. This transmission signal is wirelessly transmitted from each antenna 22a, 22b. In this way, a method for modulating a digital signal with a difference in amplitude is called an ASK (Amplitude Shift Keying) modulation method.

  When receiving the reference signal from the reference oscillator 41, the phase shifter 42 shifts the phase of the signal by 90 °. Therefore, the transmission signal from the transmission antenna 22a is in phase with the reference signal as shown in the upper part of FIG. 3B, whereas the transmission signal from the transmission antenna 22b is shown in the lower part of FIG. The signal is 90 degrees out of phase with respect to the reference signal.

  As shown in FIG. 4, the in-vehicle control unit 21 modulates a request signal, which is a transmission signal, through the LF transmission unit 22, and wirelessly transmits the request signal through the transmission antenna 22a. Since this request signal is transmitted through the transmission antenna 22a, it is in phase with the reference signal. A response signal is returned from the electronic key 10 that has received the request signal.

  As shown in FIG. 1, the UHF receiver 24 receives a response signal via the reception antenna 24a. Then, the UHF receiver 24 demodulates the response signal and outputs it to the in-vehicle controller 21. When the vehicle-mounted control unit 21 recognizes the response signal, the vehicle-mounted control unit 21 collates the ID code included in the signal with the ID code stored in the memory 21a.

  When the verification of the ID code is established, the in-vehicle control unit 21 continuously modulates the first phase signal and the second phase signal through the LF transmission unit 22 by the method described above. Specifically, when modulating the first phase signal, the modulator 43 performs on / off control of the switch 44a while keeping the switch 44b off. The modulated first phase signal is transmitted from the transmission antenna 22a. In addition, when modulating the second phase signal, the modulator 43 performs on / off control of the switch 44b while keeping the switch 44a off. The modulated second phase signal is transmitted from the transmission antenna 22b. Therefore, there is a 90 ° difference in phase between both phase signals. Note that the termination bit in the first phase signal and the leading bit in the second phase signal are set to logic “1”.

  As will be described in detail later, the electronic key 10 determines whether or not there is a correct phase difference between the two phase signals based on the received both phase signals, and thus whether or not the communication is unauthorized communication using a repeater. A determination is made, and the determination result is returned as a result signal.

  The UHF receiving unit 24 demodulates the result signal received through the receiving antenna 24 a and outputs it to the in-vehicle control unit 21. When the in-vehicle control unit 21 determines that it is not an unauthorized communication using the repeater through the result signal, the vehicle-mounted control unit 21 enters a locking / unlocking permission state. When the lock switch 31 is operated in this locking / unlocking permitted state, the in-vehicle control unit 21 switches the locking / unlocking state of the vehicle door. On the other hand, when the in-vehicle control unit 21 determines that the communication is an unauthorized communication using the repeater through the result signal, the vehicle-mounted control unit 21 does not enter the locking / unlocking permission state. This restricts the vehicle door from being unlocked by unauthorized communication using a repeater.

<Electronic key>
As shown in FIG. 1, the electronic key 10 includes an electronic key control unit 11, a limit amplifier 57, a waveform shaping unit 58, a reception antenna 12a, a detection circuit 14, a UHF transmission unit 13, and a transmission antenna 13a. Is provided.

  The electronic key control unit 11 is configured by a computer unit and includes a nonvolatile memory 11a. An ID code unique to the electronic key 10 is stored in the memory 11a.

  When receiving each phase signal, the receiving antenna 12 a outputs it to the limit amplifier 57 and the detection circuit 14. The detection circuit 14 detects the request signal received via the reception antenna 12 a and outputs it to the electronic key control unit 11. When the electronic key control unit 11 recognizes the request signal, the electronic key control unit 11 generates a response signal including an ID code stored in its own memory 11 a and outputs it to the UHF transmission unit 13. The UHF transmitter 13 modulates the response signal and transmits it as a radio signal in the UHF (Ultra High Frequency) band via its own transmission antenna 13a.

  The limit amplifier 57 amplifies each phase signal, thereby converting the waveform into a substantially trapezoidal waveform and outputs it to the waveform shaping unit 58. As shown in FIG. 7B, the waveform shaping unit 58 shapes each phase signal into a rectangular wave (pulse wave) and outputs it to the electronic key control unit 11.

  As shown in FIG. 6, this pulse wave is generated at the same frequency (125 kHz) as that of the reference signal only in a period in which the bit is 1 (period corresponding to switch-on in FIG. 3C). Further, the pulse wave is not generated in a period in which the bit is 0 (a period corresponding to switching off in FIG. 3C).

  The pulse period is calculated as the reciprocal of the frequency. Therefore, in this example, the pulse period is 1 / (125 k) seconds. In addition, the electronic key control unit 11 includes a process determination unit 50 that determines the presence / absence of a phase difference between both received phase signals and the time for which the phase difference is detected. As shown in FIG. 5, the process determination unit 50 includes a clock recovery unit 51, a phase comparison unit 52, a phase difference determination unit 53, an authentication processing unit 54, and a signal processing unit 55.

  When the clock regeneration unit 51 receives a signal for 100 pulses from the waveform shaping unit 58, the clock regeneration unit 51 regenerates the signal with a delay of 100 pulses. These 100 pulses are an example and can be changed by setting.

  For example, it is assumed that the clock recovery unit 51 receives a first phase signal for 150 pulses, and then receives a second phase signal for 10 pulses whose phase is delayed by 90 ° with respect to the same signal. In this case, when receiving the first phase signal for 100 pulses, the clock recovery unit 51 starts reproducing the signal. As shown in FIG. 7A, the clock recovery unit 51 receives the second phase signal after receiving the first phase signal for 150 pulses, and the first phase is not delayed for a while. Play the phase signal. Therefore, the phase comparison unit 52 receives signals having different phases from the clock reproduction unit 51 and the waveform shaping unit 58, that is, the reproduced first phase signal and the currently received second phase signal. The phase comparison unit 52 performs an AND operation on the signals from the clock recovery unit 51 and the waveform shaping unit 58 as shown in FIG. That is, the phase comparison unit 52 outputs Hi to the phase difference determination unit 53 only when the voltage V from both the clock recovery unit 51 and the waveform shaping unit 58 is Hi (logic “1”). In other cases, Lo (logic “0”) is output to the phase difference determination unit 53. Accordingly, the region indicated by the alternate long and short dash line in FIG. 7C is removed. The phase difference determination unit 53 determines the presence or absence of a phase difference based on the signal from the phase comparison unit 52. Specifically, when there is no phase difference, the duty ratio of the signal is about 50%, but when the phase difference reaches 90 °, the duty ratio decreases to about 25% as shown on the right side of FIG. 7C. To do. The phase difference determination unit 53 outputs a determination result based on the duty ratio to the authentication processing unit 54.

  On the other hand, as shown in FIG. 8, the detection circuit 14 detects both phase signals received via the reception antenna 12 a into “0” and “1” signals, and outputs them to the signal processing unit 55. The signal processing unit 55 recognizes the first bit Bx of the second phase signal by counting the number of bits of the signal from the detection circuit 14. Then, the signal processing unit 55 notifies the authentication processing unit 54 of a certain time T from the start of the bit Bx as a period during which the phase difference is detected. Here, both phase signals are set so that the bit Bx and the previous bit are “1”. For example, when the bit before the bit Bx (the terminal bit of the first phase signal) is “0”, the clock recovery unit 51 cannot receive a signal of 100 pulses serving as a playback source, and therefore at a certain time T. A signal containing a pulse cannot be reproduced. For example, when the bit Bx (the first bit of the second phase signal) is “0”, a signal including a pulse is not output from the waveform shaping unit 58 to the phase comparison unit 52. In any case, there is no comparison target in the phase comparison unit 52. Therefore, it is necessary to set both phase signals as described above.

  The authentication processing unit 54 determines whether or not there is a 90 ° phase difference between the two phase signals based on the determination result of the phase difference determination unit 53 at a certain time T. The electronic key control unit 11 generates a result signal including the determination result by the authentication processing unit 54 and outputs it to the UHF transmission unit 13. The UHF transmission unit 13 modulates the result signal and transmits it as a UHF band radio signal via its own transmission antenna 13a. As described above, the locking / unlocking of the vehicle door is permitted or restricted based on the result signal.

  Here, the repeater has a method of once detecting a radio signal in the LF band from a vehicle and transmitting a radio signal generated based on the detected signal. This method can be relayed with a stronger radio wave than a method of frequency conversion without detection. For this reason, it is used particularly when relaying radio signals in the LF band. However, in this method, only the envelope of the signal is taken out at the time of detection, but the phase of the signal is not copied. Therefore, even if it receives both phase signals from which a phase differs, a repeater will relay both phase signals by the same phase. Thereby, in the case of unauthorized communication using a repeater, it is determined that there is no phase difference between both phase signals, and the locking and unlocking of the vehicle door is restricted.

As described above, according to the embodiment described above, the following effects can be obtained.
(1) The phases of both phase signals are set to be different from each other. Here, even if the in-vehicle device 20 and the electronic key 10 are located far away from each other, the vehicle door may be unlocked by illegally establishing communication using the repeater. Generally, when relaying a radio signal in the LF band, the repeater detects a received radio signal once, generates a radio signal having a stronger radio wave based on the detected signal, and transmits it. When the received radio signal (phase signal) is subjected to envelope detection, the phases that differ between the two phase signals become the same phase. For this reason, in the case of unauthorized communication using a repeater, it is determined that the phase between the received two phase signals is not different, and unlocking of the vehicle door is restricted. Thereby, security can be improved.

  (2) The clock regeneration unit 51 performs signal regeneration with a certain amount (100 pulses) of delay relative to the input signal. Immediately after the input signal is switched from the first phase signal to the second phase signal, The signal is reproduced with the phase of the phase signal of 1. For this reason, immediately after switching from the first phase signal to the second phase signal, two signals having different phases are input to the phase comparator 52. Here, since the bit at the boundary portion in both phase signals is “1”, two comparison objects in the phase comparison unit 52 are surely present immediately after switching from the first to the second phase signal. The phase difference determination unit 53 determines the phase difference based on the comparison result of the phase comparison unit 52. If it is not an unauthorized communication using a repeater, it is determined through the phase difference determination unit 53 that a phase difference has occurred between both phase signals at a certain time T. When this determination is made, unlocking of the vehicle door is permitted. Further, in the case of unauthorized communication using a repeater, it is determined that there is no difference in phase between both phase signals through the phase difference determination unit 53 at a certain time T, and unlocking of the vehicle door is restricted. The Thereby, security can be improved.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, both phase signals received by the electronic key are transmitted to the vehicle side as UHF band signals, and the presence or absence of a phase difference is determined on the vehicle side based on these signals. Is different. Hereinafter, a description will be given focusing on differences from the first embodiment.

  As shown in FIG. 9, the electronic key 10 includes amplifiers 61 and 62, an RSSI (Receive Signal Strength Indication) detection circuit 63, an AND circuit 64, an oscillation unit 65, a switch 66, and a diode 67. . As shown in FIG. 10A, the amplifier 61 amplifies the LF band signal received via the receiving antenna 12a and outputs it to the detection circuit 14 and the diode 67. The detection circuit 14 detects the signal from the amplifier 61 and outputs it to the electronic key control unit 11. When recognizing that the signal from the detection circuit 14 is a request signal, the electronic key control unit 11 transmits a response signal through the UHF transmission unit 13 and the transmission antenna 13a, as in the first embodiment.

  10B, the diode 67 removes the negative component from the signal from the amplifier 61 and outputs it to the RSSI detection circuit 63. The RSSI detection circuit 63 outputs a permission signal to the AND circuit 64 when the voltage V of the signal from the diode 67 exceeds a certain value.

  On the other hand, the electronic key control unit 11 can recognize the reception period of both phase signals based on the transmission timing of the response signal. The electronic key control unit 11 outputs a permission signal to the AND circuit 64 and the oscillation unit 65 during the reception period of both phase signals. When receiving the permission signal, the oscillating unit 65 generates an unmodulated signal in the UHF band. The AND circuit 64 changes the switch 66 from the OFF state to the ON state when receiving the permission signal from both the RSSI detection circuit 63 and the electronic key control unit 11. As a result, as shown in FIG. 10C, the received LF-band both phase signals can be ASK modulated. The modulated signal is amplified by the amplifier 62 and then wirelessly transmitted through the transmission antenna 13a.

  In the present embodiment, as shown in FIG. 9, a process determination unit 50 is provided in the in-vehicle control unit 21. In addition, an envelope detector 68 is provided between the receiving antenna 24a and the limit amplifier 57 in place of the detection circuit 14 in the first embodiment. The process determination unit 50, the limit amplifier 57, and the waveform shaping unit 58 are configured in the same manner as in the first embodiment.

  The envelope detector 68 performs envelope detection on both phase signals received through the receiving antenna 24a. As a result, as shown in FIG. 10D, a waveform is obtained in which only the envelope of FIG. 10C is extracted. This waveform has the same frequency and phase as the phase signal in the LF band shown in FIG. Therefore, as in the first embodiment, it is possible to determine whether there is a 90 ° phase difference between the two phase signals at a certain time T through the processing determination unit 50 or the like, and when there is no phase difference. Is an unauthorized communication using a repeater, and the unlocking of the vehicle door is restricted.

As described above, according to the embodiment described above, the following effects can be obtained in addition to the effects (1) and (2) of the first embodiment.
(3) By providing the in-vehicle device 20 with the process determination unit 50 and the like, the electronic key 10 requiring higher portability can be configured in a compact manner.

In addition, the said embodiment can be implemented with the following forms which changed this suitably.
In both the above embodiments, the second phase signal is transmitted after the first phase signal. However, the first and second phase signals may be repeatedly transmitted alternately. Also in this case, the bit at the boundary between both phase signals is set to “1”. Thereby, in one communication, the presence or absence of a phase difference can be determined multiple times.

  In both the above embodiments, the first phase signal and the second phase signal are transmitted when the ID code is verified by receiving the response signal. However, both phase signals may be transmitted after the request signal. In this case, a determination result as to whether or not there is a phase difference between both phase signals can be included in the response signal. Therefore, the result signal can be omitted. Further, the request signal may be a phase signal, and the phase of the request signal may be shifted by 90 ° at a predetermined timing. In this case, it is not necessary to transmit both phase signals separately from the request signal.

  The phase difference between both phase signals in both the above embodiments is 90 °, but the phase difference is not limited to 90 °. As the phase difference between the two phase signals changes, the judgment criterion in the phase difference judgment unit 53 changes.

  In both the above embodiments, the first phase signal and the second phase signal are continuously transmitted. However, you may transmit a 1st phase signal and a 2nd phase signal simultaneously via both transmission antennas 22a and 22b. In this case, it is possible to determine whether or not the communication is unauthorized using a repeater based on the change in RSSI accompanying the phase difference between the two phase signals. Specifically, the RSSI in the electronic key 10 increases when both phase signals are in phase. Further, when both phase signals are in opposite phases, interference is caused and the RSSI in the electronic key 10 is reduced. From such a tendency, it is possible to determine whether or not the communication is unauthorized using the phase difference and thus using the repeater based on the RSSI. In this configuration, the time required to transmit both phase signals can be shortened. In addition, the presence or absence of a phase difference between both phase signals can be easily determined through RSSI.

  In both the above embodiments, the first phase signal is transmitted from the transmission antenna 22a, and the second phase signal is transmitted from the transmission antenna 22b. However, there may be one transmission antenna. In this case, the first phase signal and the second phase signal are transmitted from a single transmission antenna. For example, in the configuration shown in FIG. 2, the terminal on the opposite side of the reference oscillator 41 in each switch 44a, 44b is connected to a single transmission antenna. As a result, a path that passes through the phase shifter 42 and a path that does not pass through are configured, and both phase signals can be sequentially transmitted from a single transmission antenna.

  In both the above embodiments, both phase signals are transmitted from the in-vehicle device 20 to the electronic key 10. However, both phase signals may be transmitted from the electronic key 10 to the in-vehicle device 20. In this case, the LF band radio signal can be transmitted from the electronic key 10 to the in-vehicle device 20, and the processing determination unit 50, the waveform shaping unit 58, and the limit amplifier 57 are provided in the in-vehicle device as in the second embodiment. 20 is provided.

  In both the above-described embodiments, when it is determined that the communication is an unauthorized communication using the repeater through the result signal, the locking / unlocking of the vehicle door is restricted, but the engine start may be restricted. Moreover, the control object of the electronic key 10 is not limited to a vehicle, and may be a door device for a house, for example. Even in this case, the unauthorized communication using the repeater can be prevented as in both the above embodiments.

  In both the above embodiments, the ASK modulation method is adopted as the digital modulation method. However, the modulation method is not limited to this. For example, an FSK (Frequency Shift Keying) modulation method or a PSK (Phase Shift Keying) modulation method is adopted. May be.

Next, the technical idea that can be grasped from the embodiment will be described together with the effects.
(A) In the communication system according to claim 3, the electronic key includes a transmission antenna that transmits a radio signal in the UHF band, an oscillation unit that generates an unmodulated signal in the UHF band, the transmission antenna, and the oscillation unit. The first and second UHF bands modulated on the basis of the unmodulated signal by turning on and off the switch according to the signal strength of the first and second phase signals of the LF band And a switch switching means for generating a phase signal of 2.

According to this configuration, the electronic key can be modulated to the UHF band while maintaining the phases of the first and second phase signals in the LF band with a simple configuration, and wirelessly transmitted.
(B) In the communication system according to (A), the electronic key includes a control unit that controls output of the non-modulated signal in the oscillation unit, and the control unit includes first and second LF bands. A communication system for outputting the non-modulated signal from the oscillating unit over a time expected to receive two phase signals.

  According to this configuration, the non-modulated signal is output from the oscillating unit only during the time when it is expected to receive the first and second phase signals in the LF band. Therefore, the useless output of the unmodulated signal is suppressed.

  (C) In the communication system according to claim 3, (a) and (b), the first communication device wirelessly transmits a request signal different from the first and second phase signals, The electronic key wirelessly transmits a response signal including its own ID code in response to the received request signal, and the first communicator is when the received ID code is verified and received A communication system that permits execution of the control when it is determined that the phases of the first and second phase signals are different.

  According to this configuration, it is necessary to further verify ID code in order to execute control. Therefore, security can be further improved.

  DESCRIPTION OF SYMBOLS 1 ... Electronic key system, 10 ... Electronic key (2nd communication apparatus, mobile communication apparatus), 11 ... Electronic key control part, 13 ... UHF transmission part, 14 ... Detection circuit, 20 ... In-vehicle apparatus (1st communication) Machine), 21 ... in-vehicle controller, 22 ... LF transmitter, 22a, 22b ... transmit antenna, 24 ... UHF receiver, 41 ... reference oscillator, 42 ... phaser, 43 ... modulator, 44a, 44b ... switch, 50 ... Processing determination unit, 51 ... Clock reproduction unit, 52 ... Phase comparison unit, 53 ... Phase difference determination unit, 54 ... Authentication processing unit, 55 ... Signal processing unit, 57 ... Limit amplifier, 58 ... Waveform shaping unit, 61,62 ... Amplifier, 63 ... RSSI detection circuit, 64 ... AND circuit (switch switching means), 65 ... oscillator, 66 ... switch, 67 ... diode, 68 ... envelope detector.

Claims (5)

In a communication system that permits control of a control object through transmission / reception of a radio signal between a first communication device and a second communication device, at least one of which is a mobile communication device,
The radio signal is transmitted from the first communication device in a time division manner or simultaneously as a radio signal in the LF band under a specific phase condition,
When it is determined that the signal received by the second communication device satisfies the specific phase condition, execution of the control is permitted as not being an unauthorized communication using a repeater, and the specific phase condition is not satisfied A communication system that prohibits execution of the control because it is illegal communication using a repeater when judged. The communication system according to claim 1,
The specific phase condition is that there is a phase difference between the first signal and the second signal transmitted in a time division manner as the radio signal,
The first or second communication device includes a process determination unit,
The process determination unit
A reproduction unit that reproduces the phase of the received first or second signal when the received first or second signal exceeds a certain level;
A phase comparison unit that compares the phase of the signal being reproduced by the reproduction unit with the phase of the first or second signal currently being received;
A phase difference determination unit that determines whether or not a phase difference of the currently received signal has occurred based on a comparison result of the phase comparison unit;
A signal processing unit for recognizing a time when a phase difference is expected to be detected in the phase difference determination unit based on a timing at which a signal being received is switched from the first signal to the second signal;
When it is determined that a phase difference has occurred through the phase difference determination unit at a time when the phase difference recognized through the signal processing unit is expected to be generated, execution of the control is permitted as an unauthorized communication using a repeater. A communication system that prohibits execution of the control as an unauthorized communication using a repeater when it is determined that no phase difference has occurred through the phase difference determination unit at a time when the phase difference is expected to occur. . The communication system according to claim 2,
The first communication device includes the processing determination unit and is provided in the vehicle to be controlled.
The second communication device is provided as an electronic key possessed by the user,
When the electronic key receives the first and second signals in the LF band transmitted from the first communication device, the electronic key sends the first and second signals in the UHF band corresponding to the signals to the first key. To the communication device,
The first communication device is a communication system in which the received first and second signals in the UHF band are detected so that these signals are in phase with the first and second signals in the LF band. The communication system according to claim 2 or 3,
A control request signal for requesting control as the radio signal is transmitted between the two communication devices,
The communication system in which the first and second signals are transmitted as phase signals separately from the control request signal. The communication system according to claim 1,
The specific phase condition is that there is a phase difference between the first signal and the second signal transmitted simultaneously as the radio signal,
The second communication device is a communication system that determines that the specific phase condition is satisfied when it is determined that there is a phase difference between the two signals based on the signal strength of the signal in which the two signals interfere with each other.

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