DISTANCE ESTIMATION SYSTEM

Abstract

Distance estimation system comprising: a first terminal (1) and a second terminal (2) which perform wireless communication of an on-off keying by transmitting and receiving pulse signals, wherein the first device contains: a data generation unit (F11) that generates response request data for requesting the second terminal to return a response signal, a first terminal-side transmitter (12) which transmits a response request signal in which the pulse signals are arranged at a predetermined transmission interval corresponding to a bit string constituting the response request data, and successively transmits the pulse signals as synchronization signals at the predetermined transmission interval during a predetermined time after the transmission of the response request signal has been terminated, and a first terminal-side receiver (13) which receives the pulse signals returned by the second terminal as the response signal to the response request signal, the second device contains: a second terminal-side receiver (23) which receives the response request signal, a response data generation unit (F22) that generates response data based on a bit string as the response request data determined by demodulating the response request signal received by the second terminal-side receiver, a transmission destination bit setting unit (F23) that shifts a bit that is a transmission destination in a bit string as the response data generated by the response data generation unit by one toward a rear side from a leading bit to a trailing bit each time the synchronization signal is received, and a second terminal-side transmitter (22) which transmits the pulse signal in a case where a value of the bit which is the transmission destination at a time of reception of a synchronization signal is a predetermined value previously determined as a value indicating that the pulse signal is to be transmitted, and does not transmit a pulse signal in a case where the value of the bit is not the predetermined value, and the first device also contains: a round trip timer (F14) which measures a time from a transmission of the synchronization signal to a reception of the pulse signal as a round trip time, and a distance estimation unit (F15) that determines a travel time during which the pulse signal has propagated through a space based on the round trip time measured by the round trip timer, and estimates a distance to the second terminal based on the travel time and a propagation speed, which is a speed at which the pulse signal propagates in the space.

Description

Technical area

[0001] The present invention relates to a technique for estimating a distance to a communication terminal other than a communication partner (hereinafter referred to as a partner station) by receiving a signal transmitted from the partner station. State of the art

[0002] Regarding a system in which a first communication terminal (hereinafter referred to as a first terminal) and a second communication terminal (hereinafter referred to as a second terminal) perform mutual wireless communication, various techniques for estimating a distance (hereinafter referred to as an inter-terminal distance) from the second terminal to the first terminal based on a condition of the first terminal receiving a signal transmitted from the second terminal have been studied.

[0003] For example, JP 2014 - 84 595 A describes a method in which a time (hereinafter referred to as round trip time) from the time at which the first terminal transmits a signal requesting a response to the second terminal until the time at which the first terminal receives the response from the second communication terminal is measured, and an inter-terminal distance is estimated based on the round trip time and a propagation speed of a radio wave.

[0004] As a communication system for the first and second terminals, ultra-wideband pulse radio (UWB-IR) using on-off keying as a modulation method is available. UWB-IR is a method for performing communication by transmitting a signal with a pulse width of a very short time period (e.g., several ns) (i.e., a pulse signal). When on-off keying is used for UWB-IR, the presence or absence of the pulse signal at a scheduled transmission or reception time indicates a bit value (i.e., 0 or 1) of digital data.

[0005] EP 2 053 756 A1 discloses a synchronization method for pulsed wireless communication between a first transceiver and a second transceiver, the method comprising the following steps: transmitting a pulse signal from a first transceiver to a second transceiver; transmitting a reflection signal from the second transceiver to the first transceiver when the transmitted pulse signal is received at the second transceiver within an active reception period of the second transceiver; and detecting the reflection pulse to determine synchronization between the first transceiver and the second transceiver.

[0006] US 2005 / 0 271 150 A1 discloses a digital modulation system and method using a communication frame containing a synchronization section. Data is modulated or encoded on the synchronization section. Summary of the invention

[0007] When the configuration is such that the second terminal does not return a signal transmitted from the first terminal as it is, but generates a response signal according to a content of the received signal and returns the generated signal, the round trip time includes a time required for arithmetic processing in the second terminal to generate the response signal according to the received signal (hereinafter referred to as required calculation time) (this is taken as an assumed configuration).

[0008] For example, in a system in which the first terminal and the second terminal perform authentication processing by a challenge-response method through wireless communication, the round trip time includes a computing time required for generating the response signal in the second terminal when a time from a completion of transmission of a challenge signal by a first terminal to a reception of a response signal is used as the round trip time.

[0009] Since the required computing time included in the round-trip time is actually not a time during which radio waves propagate, if the round-trip time is assumed to be a time during which radio waves propagate as they are (so-called flight time) and an inter-terminal distance is calculated, an error corresponding to a length of the required computing time will occur in the calculated inter-terminal distance.

[0010] To deal with such a problem, an error of an estimated inter-terminal distance with respect to an actual value can be reduced to some extent if an assumed value of the required computing time is predetermined in the second terminal and the assumed value of the required computing time is excluded from a measured round-trip time.

[0011] However, an error corresponding to the accuracy of a clock oscillator disposed in the second terminal device is present in an error between a design value of the required computing time and the actual value. Depending on the accuracy of a clock oscillator disposed in the first terminal device, a time measured as a round-trip time also contains an error. The influence of such an error, which occurs depending on the accuracy of each clock oscillator, accumulates and increases as the required computing time or the total round-trip time is longer.

[0012] Needless to say, the larger the error inherent in the round-trip time, the larger the error in the travel time determined from the round-trip time. Since the travel time error affects the accuracy of the estimated inter-device distance, a smaller travel time error is advantageous.

[0013] The present invention has been made in view of the above aspects, and its object is to provide a distance estimation system capable of more accurately estimating a distance between a first communication terminal and a second communication terminal.

[0014] A distance estimation system according to one aspect of the invention includes a first terminal and a second terminal that perform on-off keying wireless communication by transmitting and receiving pulse signals. The first terminal includes a data generation unit that generates response request data for requesting the second terminal to return a response signal, a first terminal-side transmitter (first terminal-side transmitter) that transmits a response request signal in which the pulse signals are arranged at a predetermined transmission interval according to a bit string constituting the response request data, and sequentially transmits the pulse signals as synchronization signals at the predetermined transmission interval during a predetermined time after the transmission of the response request signal is completed, and a first terminal-side receiver (first terminal-side receiver).which receives the pulse signals returned from the second terminal as the response signal to the response request signal. The second terminal includes a second terminal-side receiver (second terminal-side receiver) that receives the response request signal, a response data generation unit that generates response data based on a bit string as the response request data determined by demodulating the response request signal received by the second terminal-side receiver, a transmission destination bit setting unit that shifts a bit representing a transmission destination in a bit string as the response data generated by the response data generation unit by one toward a trailing side from a leading bit to a trailing bit each time the synchronization signal is received, and a second terminal-side transmitter (second terminal-side transmitter).which transmits the pulse signal in a case where a value of the bit that is the transmission destination at the time of receiving a synchronization signal is a predetermined value previously determined as a value indicating that the pulse signal is to be transmitted, and does not transmit a pulse signal in a case where the value of the bit is not the predetermined value. The first terminal device also includes a round-trip timer that measures a time from transmission of the synchronization signal to reception of the pulse signal as a round-trip time, and a distance estimation unit that determines a travel time during which the pulse signal has propagated through a space based on the round-trip time measured by the round-trip timer, and estimates a distance to the second terminal device based on the travel time and a propagation speed, which is a speed at which the pulse signal propagates in the space.

[0015] According to the distance estimation system, the distance between the first communication terminal and the second communication terminal can be estimated more accurately. Short description of the drawings

[0016] The above and other objects, features, and advantages of the present invention will become apparent from the following detailed description with reference to the accompanying drawings. Fig. 1 is a block diagram showing a schematic configuration of a distance estimation system; Fig. 2 is a functional block diagram showing a schematic configuration of a first terminal-side controller (first terminal-side controller); Fig. 3 is a diagram for explaining a modulation method used by the distance estimation system; Fig. 4 is a functional block diagram showing a schematic configuration of the first terminal-side controller; Fig. 5 is a flowchart for explaining an operation of a second terminal-side controller (second terminal-side controller); Fig. 6 is a diagram for explaining an operation of the distance estimation system of the present embodiment; and Fig. 7 a diagram showing operation of a comparison configuration. Description of the embodiments

[0017] Embodiments of the present invention will now be described with reference to the drawings. Fig. 1 is a diagram illustrating an example of a schematic configuration of a distance estimation system 100 according to the present embodiment. As shown in Fig. 1, the distance estimation system 100 includes a first terminal 1, which is a first communication terminal, and a second terminal 2, which is a second communication terminal.

[0018] The first terminal 1 can be carried by a user or can be mounted on a moving body such as a vehicle. The first terminal 1 can also be fixed to a road, a facility, or the like. The first terminal 1 can also be a portable device. The same applies to the second terminal 2. If the first terminal 1 and the second terminal 2 are not distinguished from each other below, each terminal will simply be referred to as a communication terminal.

[0019] The first terminal 1 and the second terminal 2 perform ultra-wideband pulsed radio (UWB-IR) communication. UWB-IR is a method for performing communication by transmitting a signal with a pulse width of a very short time (several ns) (i.e., a pulse signal).

[0020] As a modulation method of wireless communication implemented by these communication terminals, on-off keying (OOK) is used to transmit information based on the presence or absence of a pulse signal. That is, the communication terminal on the transmitting side transmits a pulse signal when transmitting a binary 1 and does not transmit a pulse signal when transmitting a binary 0. An interval (hereinafter, "transmission interval") in the case of continuous transmission of the pulse signal is predetermined. The transmission interval may be, for example, 1 ms.

[0021] When receiving the pulse signal, the communication terminal on the receiving side detects that a binary 1 has been received. When not receiving the pulse signal at a position on a time axis (hereinafter referred to as the scheduled reception position) where reception of a pulse signal is scheduled, the communication terminal on the receiving side detects a binary 0. The scheduled reception position is arranged for each transmission interval with respect to the time at which the pulse signal is received. Needless to say, the scheduled reception position can be determined by synchronization between communication terminals using a known method. (Configuration of the first device 1)

[0022] First, a configuration of the first terminal 1 is described. As it is in Fig. 1, the first terminal device 1 includes a first terminal-side controller 11, a first terminal-side transmitter 12, and a first terminal-side receiver 13. The first terminal-side controller 11 is communicatively connected to the first terminal-side transmitter 12 and the terminal-side receiver 13, respectively.

[0023] The first terminal-side controller 11 is a module for controlling operations of the first terminal-side transmitter 12 and the first terminal-side receiver 13. The first terminal-side controller 11 is configured as a normal computer including a CPU 111, a RAM 112, a ROM 113, a clock oscillator 114, and a bus line connecting these components.

[0024] The CPU 111 is a central processing unit obtained using a microprocessor or the like. The RAM 112 is a volatile memory, and the ROM 113 is a non-volatile memory. The ROM 113 stores a program (hereinafter referred to as the first terminal program) for causing a normal computer to serve as the first terminal 1. The clock oscillator 114 sequentially outputs a clock signal having a predetermined operating frequency. An oscillator having a desired operating frequency and accuracy can be used as the clock oscillator 114. For example, a crystal oscillator, a rubidium oscillator, or the like can be used as the clock oscillator 114.

[0025] Note that the above first terminal program may be stored in a non-volatile storage medium. Execution of the first terminal program by the CPU 111 corresponds to execution of a process corresponding to the first terminal program.

[0026] The first terminal-side controller 11 generates data (hereinafter, transmission data) to be transmitted to the second terminal 2, and transmits a pulse train signal corresponding to the transmission data to the second terminal 2 in cooperation with the first terminal-side transmitter 12. Note that the pulse train signal here means a signal train generated by modulating the transmission data by on-off keying, in which a plurality of pulse signals are arranged at predetermined time intervals. Furthermore, the first terminal-side controller 11 acquires the data received by the first terminal-side receiver 13. The functions and operations of the first terminal-side controller 11 will be described later.

[0027] The first terminal-side transmitter 12 has an antenna 121 for transmitting a pulse signal. The first terminal-side transmitter 12 sequentially transmits pulse signals based on an instruction from the first terminal-side controller 11. Specifically, when an electrical pulse signal is input from the first terminal-side controller 11, the pulse signal is amplified and shaped to be output to the antenna 121 and radiated as a radio wave.

[0028] The first terminal-side receiver 13 includes an antenna 131 for receiving the pulse signal transmitted from the second terminal 2. The first terminal-side receiver 13 receives the pulse signal transmitted from the second terminal 2 via the antenna 131, shapes or amplifies the pulse signal, and outputs the pulse signal to the first terminal-side controller 11. (Functions in the first terminal-side control 11)

[0029] As it is in Fig. As shown in FIG. 2, the first terminal-side controller 11 includes, as functions to be achieved by the CPU 111 executing the first terminal program, a data generation unit F11, a transmission processing unit F12, a reception processing unit F13, a round-trip timer F14, and a distance estimation unit F15. Note that some or all of the functional blocks of the first terminal-side controller 11 may be realized in hardware using one or more integrated circuits (ICs).

[0030] The data generation unit F11 is a functional block for generating data to be transmitted to the second terminal 2 (i.e., transmission data). Among the various transmission data pieces generated by the data generation unit F11, data requesting the second terminal 2 to return a response signal is referred to as response request data.

[0031] Here, as an example, it is assumed that the data generation unit F11 is capable of generating plural types of response request data. More specifically, the data generation unit F11 according to the present embodiment generates data in which a bit string (i.e., bit pattern) is set to "11011" as one response request data piece. In addition, data of a character string consisting of "10101" is generated as another response request data piece. A transmission condition for each response request data piece can be appropriately designed, for example, in which case the response request data is generated and the pulse train signal corresponding to the data is transmitted in cooperation with the first terminal-side transmitter 12. Note that a bit number and the bit pattern constituting the response request data can be appropriately designed.

[0032] As described later, when the second terminal 2 receives the response request data, it generates response data corresponding to a content (more precisely, a bit pattern) of the received response request data. Then, the pulse train signal corresponding to the generated response data is returned to the first terminal 1.

[0033] The transmission processing unit F12 modulates the transmission data generated by the data generation unit F11 by on-off keying. As shown in Fig. 3, the transmission data is converted into a pulse train signal in which pulse signals with an extremely narrow time width (ie, pulse signals) are arranged, in accordance with a value of each bit (specifically, 1 or 0) constituting the transmission data. Note that Tps, which is shown in Fig. 3 represents the transmission interval described above.

[0034] Then, the transmission processing unit F12 sequentially outputs the pulse signals constituting the pulse train signal generated as described above to the first terminal-side transmitter 12. Thus, the pulse train signal generated by the transmission processing unit F12 is radiated as a radio wave from the antenna 121. Note that the pulse train signal obtained by modulating the response request data corresponds to the response request signal.

[0035] After sending out the transmission data, the transmission processing unit F12 successively sends out the pulse signals as synchronization signals at the transmission interval Tps described above for a fixed time (for example, several tens of milliseconds) from a time point at which a predetermined waiting time Tw has elapsed.

[0036] The reception processing unit F13 acquires the pulse train signal transmitted from the second terminal 2 based on the pulse signal input from the first terminal-side receiver 13. The pulse train signal acquired by the reception processing unit F13 is a signal obtained by arranging a plurality of pulse signals input from the first terminal-side receiver 13 in time sequence at an actual reception interval.

[0037] The reception processing unit F13 demodulates the received pulse train signal and re-stores the data transmitted from the second terminal 2. That is, the reception processing unit F13 obtains data (ie, response data) obtained by demodulating the reception signal.

[0038] The round trip timer F14 is a timer that measures the time (hereinafter referred to as the round trip time) from the time the first terminal-side transmitter 12 transmits the synchronization signal to the time the first terminal-side receiver 13 receives the pulse signal returned from the second terminal 2. The round trip timer F14 counts the clock signals input from the clock oscillator 114 to measure an elapsed time since the synchronization signal is transmitted. The count value of the round trip timer F14 returns to 0 (i.e., the count value is reset) each time the synchronization signal is transmitted. Therefore, the time held by the round trip timer F14 corresponds to the elapsed time since the last transmission of the synchronization signal.

[0039] The distance estimation unit F15 estimates a distance between the first terminal 1 and the second terminal 2 (hereinafter, the inter-terminal distance) based on the round-trip time obtained by the round-trip timer F14. The details of the distance estimation unit F15 will be described later. (Configuration of the second device 2)

[0040] The following describes a configuration of the second terminal 2. As shown in Fig. 1, the second terminal 2 includes a second terminal-side controller 21, a second terminal-side transmitter 22, and a second terminal-side receiver 23. The second terminal-side controller 21 is communicatively connected to the second terminal-side transmitter 22 and the second terminal-side receiver 23, respectively.

[0041] The second terminal-side controller 21 is a module for controlling operations of the second terminal-side transmitter 22 and the second terminal-side receiver 23. The second terminal-side controller 21 is configured as a normal computer including a CPU 211, a RAM 212, a ROM 213, a clock oscillator 214, and a bus line connecting these components. Components having the same names as those of the first terminal 1, such as the CPU 211, have the same functions as those in the first terminal 1. The ROM 213 stores a program (hereinafter referred to as a second terminal program) for causing a normal computer to function as the second terminal 2.

[0042] The functions and operations of the second terminal-side controller 21 will be described separately later, but are schematically as follows. The second terminal-side controller 21 acquires the data received by the second terminal-side receiver 23. Then, upon acquiring the response request data transmitted from the first terminal 1, the second terminal-side controller 21 generates response data corresponding to the response request data and returns the response data to the first terminal 1 in cooperation with the second terminal-side transmitter 22.

[0043] The second terminal-side transmitter 22 includes an antenna 221 for transmitting a pulse signal and transmits the pulse signal based on an instruction from the second terminal-side controller 21. The second terminal-side receiver 23 includes an antenna 231 for receiving the pulse signal transmitted from the second terminal 2. The second terminal-side receiver 23 receives the pulse signal transmitted from the second terminal 2 via the antenna 231, shapes or amplifies the pulse signal, and outputs the pulse signal to the second terminal-side controller 21. (Functions in the second terminal-side control 21)

[0044] As it is in Fig. As shown in FIG. 4, the second terminal-side controller 21 includes, as functional blocks to be achieved by the CPU 211 executing the second terminal program, a reception processing unit F21, a response data generation unit F22, a transmission destination bit setting unit F23, and a transmission processing unit F24. Note that some or all of the functional blocks of the second terminal-side controller 21 may be realized in hardware using one or more ICs.

[0045] The reception processing unit F21 acquires the pulse train signal (e.g., response request signal) transmitted from the first terminal 1 based on the pulse signal input from the second terminal-side receiver 23. The reception processing unit F21 then demodulates the received pulse train signal and re-stores the data transmitted from the first terminal 1. That is, the reception processing unit F21 acquires data (i.e., response request data) obtained by demodulating the reception signal.

[0046] The response data generation unit F22 generates response data corresponding to the response request data acquired by the reception processing unit F21. For example, when receiving response request data with a bit string of "11011," the response data generation unit F22 generates a bit string consisting of "1010101" as response data. When receiving response request data with a bit string of "10101," the response data generation unit F22 generates a bit string consisting of "1110111" as response data.

[0047] Which type of response data is generated for which type of response request data can be appropriately designed or configured. The design only needs to be such that the response data to be generated by the response data generation unit F22 is uniquely determined with respect to the received response request data. The response data generated by the response data generation unit F22 is provided to the transmission destination bit setting unit F23.

[0048] The transmission destination bit setting unit F23 shifts a bit that is a transmission destination by one toward a trailing side from a leading bit to a trailing bit of a bit string constituting the response data of the response data generation unit F22 each time the synchronization signal is received. When the value of the transmission destination bit is 1, the transmission destination bit setting unit F23 sets the transmission processing unit F24 to a transmission preparation mode. On the other hand, when the value of the transmission destination bit is 0, the transmission destination bit setting unit F23 sets the transmission processing unit F24 to a transmission hold mode.

[0049] The transmission processing unit F24 includes the transmission preparation mode and the transmission hold mode as operation modes. In a case where the transmission preparation mode has been set by the transmission target bit setting unit F23, the reception processing unit F21 outputs the pulse signal to be transmitted as a radio wave to the second terminal-side transmitter 22 when the reception processing unit F21 receives a synchronization signal. On the other hand, in a case where the transmission hold mode has been set by the transmission target bit setting unit F23, even if the reception processing unit F21 receives a synchronization signal, the reception processing unit F21 does not output the pulse signal to the second terminal-side transmitter 22.

[0050] That is, when receiving reception response request data, the second terminal-side controller 21 is executed as shown in the flowchart of Fig. 5. First, in S101, the response data generation unit F22 generates response data corresponding to a content of the received response request data, and then the processing proceeds to S102.

[0051] In S102, the transmission destination bit setting unit F23 sets (i.e., initializes) a variable j used for subsequent processing to 1, and then the processing proceeds to S103. Note that a positive integer is set for the variable j.

[0052] In S103, the transmission destination bit setting unit F23 determines whether a value of a j-th bit of the response request data is equal to 1. For example, when j = 1, it is determined whether the leading bit of the response request data is equal to 1. If the value of the j-th bit of the response request data is equal to 1, the result of the determination in S103 is positive, and then the processing proceeds to S104. If the value of the j-th bit of the response request data is not equal to 1, that is, if the value of the j-th bit is equal to 0, the result of the determination in S103 is negative, and the processing proceeds to S107.

[0053] In step S104, the transmission target bit setting unit F23 sets the operation mode of the transmission processing unit F24 to the transmission preparation mode, and then the processing proceeds to S105. In S105, the reception processing unit F21 waits until it receives the synchronization signal. If the synchronization signal is received, the processing proceeds to S106. If the synchronization signal is not received even after a predetermined time has elapsed since the transition to S105, the current flow may be terminated. In S106, the transmission processing unit F24 outputs the pulse signal to the second terminal-side transmitter 22 to transmit the pulse signal as a radio wave, and then the processing proceeds to S109. That is, when the value of the transmission target bit is 1, the pulse signal is transmitted, with the reception of the synchronization signal serving as the trigger.

[0054] Note that a method for identifying whether the received pulse signal is a synchronization signal or a pulse signal as part of data can be appropriately configured. In the present embodiment, according to one example, the reception processing unit F21 is configured to determine that the pulse signal received within a fixed time after receiving the response request data is not a pulse signal as part of the data, but is a synchronization signal.

[0055] Needless to say, the method for identifying whether the received pulse signal is a synchronization signal or a piece of data is not limited to the above example. For example, a bit string indicating that transmission of a synchronization signal will start may be placed at the end of the data transmitted from the first terminal 1 to cause the second terminal 2 to recognize that the pulse signal received within a fixed time after the end is a synchronization signal.

[0056] In S107, the transmission target bit setting unit F23 sets the operation mode of the transmission processing unit F24 to the transmission hold mode, and then the processing proceeds to S108. In S108, the reception processing unit F21 waits until it receives the synchronization signal. When the reception processing unit F21 receives the synchronization signal, the processing proceeds to S109. That is, if the value of the transmission target bit is 0, the pulse signal is not transmitted. If the synchronization signal is not received even after a predetermined time has elapsed since the transition to S108, the current flow can be terminated.

[0057] In S109, it is determined whether the value of variable j is less than a bit number n of the response data. If the value of variable j is less than the bit number n of the response data, the result of the determination in S109 is positive, and then the processing proceeds to S110. On the other hand, if the value of variable j is not less than the bit number n of the response data, the result of the determination in S110 is negative, and then the current flow is terminated. The bit number n here is equal to 7. In S110, the transmission destination bit setting unit F23 adds 1 to the value of j (ie, increments) and returns to S103.

[0058] Note that the case where the value of variable j is less than the number of bits n of the response data indicates a state in which the response data has not been completely transmitted. The case in which the value of variable j is not less than the number of bits n of the response data indicates a state in which the transmission of the response data has been completed. (Operation of the distance estimation system)

[0059] The operation of the distance estimation system 100 of the present embodiment will be described below with reference to Fig. 6. Here, according to an example, the operations of the first terminal 1 and the second terminal 2 are described, assuming a case where the first terminal 1 transmits response request data with a bit pattern of "11011". Note that a horizontal axis of the various diagrams in Fig. 6 represents the passage of time.

[0060] When the data generation unit F11 of the first terminal 1 generates the response request data consisting of the bit string “11011” as shown in Fig. As shown in Figure 6, the first terminal-side transmitter 12 transmits a pulse train signal corresponding to the response request data as a response request signal. As described above, the pulse train signal as the response request signal is a signal train in which each pulse signal is arranged at a position corresponding to a bit where a binary 1 is set in the response request data.

[0061] Furthermore, based on an instruction from the transmission processing unit F12, the first terminal-side transmitter 12 starts transmitting the pulse signal as a synchronization signal from a time point T2 at which a predetermined waiting time Tw has elapsed since a time point T1 at which the transmission of the response request signal was terminated, with the transmission interval Tps. The waiting time Tw may be set to a length corresponding to an assumed value (ie, a design value) of a required computing time Tcl, which will be described later, and may be set, for example, to a length of 70% of the assumed value of the required computing time Tcl. The state in which the first terminal 1 periodically transmits the synchronization signal may be continued for a predetermined time (hereinafter: transmission continuation time).The transmission continuation time may be appropriately designed based on the maximum value of a time it takes from completion of transmission of the response request signal to reception of the response signal returned from the second terminal 2.

[0062] Based on a clock signal input from the clock oscillator 114, the round trip timer F14 starts measuring the time elapsed since the first terminal-side transmitter 12 transmitted the synchronization signal. As described above, the count value of the round trip timer F14 is reset each time the synchronization signal is transmitted.

[0063] Each pulse signal constituting the response request signal transmitted from the first terminal-side transmitter 12 is received by the second terminal-side receiver 23 with a propagation delay Tf relative to the transmission time. The propagation delay Tf is a time it takes for a radio wave to propagate from the first terminal 1 to the second terminal 2 and is proportional to the inter-terminal distance. Specifically, the propagation delay Tf corresponds to a value obtained by dividing the inter-terminal distance by a propagation velocity C of the radio wave. The propagation velocity C in the air is 3 × 10 8 (ie 3 × 10 to the eighth power) [m / s].

[0064] When the reception processing unit F21 of the second terminal 2 has finished receiving a sequence of pulse train signals as a response request signal, the reception processing unit F21 demodulates the pulse train signal to generate reception data. Then, the response data generation unit F22 generates response data corresponding to a content of the received data (ie, response request data). Upon receiving the bit string "11011" as response request data, the response data generation unit F22 generates a bit string consisting of "1010101" as response data.

[0065] Note that the processing for determining the content of the received data (ie, response request data) and generating the response data according to the content corresponds to arithmetic processing. Tcl, which is used in Fig. 6 represents a time required for arithmetic processing (hereinafter referred to as required calculation time).

[0066] Then, the transmission processing unit F24, in cooperation with the transmission target bit setting unit F23, transmits a pulse signal or no pulse signal in order from a first bit of the response data according to the value of the transmission target bit in synchronization with reception of the synchronization signal. Specifically, the pulse signal is transmitted when the value of the transmission target bit is a predetermined value previously determined as a value for transmitting the pulse signal, and the pulse signal is not transmitted when the value is not the predetermined value. When the transmission processing unit F24 is in the transmission preparation mode, Td shown in the figure represents an internal transmission time from reception of the pulse signal as a synchronization signal by the second terminal-side receiver 23 to transmission of the pulse signal by the second terminal-side transmitter 22.

[0067] This internal transmission time Td is derived from the transmission time of the pulse signal from the second transmitting-side receiver 23 to the second terminal-side controller 21, the transmission time of the pulse signal from the second terminal-side controller 21 to the second terminal-side transmitter 22, or any other time. The internal transmission time Td may also include a time until the second terminal-side controller 21 detects the input of the pulse signal from the second terminal-side receiver 23 and outputs a pulse signal. However, the internal transmission time Td is sufficiently shorter than the required computing time Tcl.

[0068] A sequence of several pulse signals, which is transmitted as a response signal by the second terminal-side transmitter 22, is received by the first terminal-side receiver 13 with a delay of the propagation time Tf with respect to the transmission time.

[0069] The round-trip timer F14 saves, as the round-trip time, a count value at a time of reception of the pulse signal by the first terminal-side receiver 13 in the RAM 112 or the like. Note that the transmission interval Tps is set to a value sufficiently larger than a time obtained by adding the propagation time Tf corresponding to the maximum value of the inter-terminal distance as a detection range and an assumed value of the internal transmission time Td.

[0070] In the example shown in Fig. As shown in Figure 6, the round trip time can be measured four times, since the second terminal-side transmitter 22 transmits a pulse train signal containing four pulse signals as a response signal. Trt1 to Trt4 in Fig. 6 each represent the round trip time recorded by the round trip timer F14.

[0071] The distance estimation unit F15 estimates an inter-terminal distance based on the round-trip time Trt1 obtained as described above. According to one example, the round-trip time is calculated by subtracting an assumed value of the current internal transmission time Td from the round-trip time Trt1. Then, a value obtained by multiplying a value obtained by dividing the round-trip time by 2 by the propagation speed C is used as the inter-terminal distance.

[0072] According to another aspect, the above-described arithmetic processing is performed on the respective round-trip times Trt1 to Trt4 to calculate a plurality of candidate inter-terminal distances and use an average value from the candidate inter-terminal distances. Alternatively, an average of the travel times may be calculated from the respective average values ​​of the round-trip times Trt1 to Trt4, and the inter-terminal distance may be calculated from the average of the travel times and the propagation speed. Needless to say, a median value may be used instead of the average value. Estimating the inter-terminal distance using the round-trip times Trt1 to Trt4 enables accuracy improvement.

[0073] The first terminal 1 can be configured such that not only the internal transmission time Td in the second terminal 2 but also the internal transmission time Td in the first terminal 1 is included in the round-trip time measured by the round-trip timer F14. In such a case, it is advantageous to use a value obtained by subtracting twice the assumed value of the internal transmission time Td from the round-trip time Trt1 as the round-trip time. (Effects of the present embodiment)

[0074] In the following, the operation and effects of the present embodiment described above will be described by introducing a comparative configuration according to the prior art. Fig. 7, in the comparison configuration, a time elapsed from the transmission of the last pulse signal forming the response request signal until the reception of the pulse signal by the first terminal-side receiver 13 is used as the round trip time. Trt_a, Trt_b, Trt_c and Trt_d, which are shown in Fig. 7 represent the round trip time (hereinafter referred to as the comparison runtime) captured by the comparison configuration.

[0075] The comparison propagation time Trt_a is calculated as a total value of the propagation time Tf of the pulse signal from the first terminal 1 to the second terminal 2, the required computing time Tcl, the internal transmission time Td, and the propagation time Tf of the pulse signal from the second terminal 2 to the second terminal 1. Furthermore, any one of the comparison propagation time Trt_b, the comparison propagation time Trt_c, and the comparison propagation time Trt_d is a value obtained by adding an integer multiple (e.g., two times, four times, six times) of the transmission interval Tps to the comparison propagation time Trt_a.

[0076] In the comparison configuration, the comparison runtime Trt_a contains an assumed value of the required computing time Tcl as the round trip time. Thus, to estimate the inter-device distance from the comparison runtime Trt_a, it is necessary to exclude the assumed value of the required computing time Tcl from the measured round trip time.

[0077] However, an error corresponding to the accuracy of the clock oscillator 214 (hereinafter, clock accuracy) disposed in the second terminal device is included in an error between a design value of the required computing time Tcl and an actual value. Furthermore, a time measured as a round-trip time depending on the accuracy of the clock oscillator 114 disposed in the first terminal device itself contains an error. Such an error resulting from the accuracy of each clock oscillator is accumulated and increases as the required computing time Tcl is longer. That is, the comparison configuration is susceptible to an error resulting from the clock accuracy.

[0078] On the other hand, the respective round-trip times Trt1 to Trt4 measured according to the present embodiment are each a total of the propagation time Tf of the pulse signal from the first terminal 1 to the second terminal 2, the internal transmission time Td, and the propagation time Tf of the pulse signal from the second terminal 2 to the first terminal 1, and do not include the required computing time Tcl or the transmission interval Tps. That is, according to the configuration of the present embodiment, the time measured as the round-trip time can be shortened compared to the comparative configuration.

[0079] As described above, the shorter the round-trip time, the less susceptible the configuration is to errors resulting from timing accuracy. Furthermore, the internal transmission time Td itself is sufficiently shorter than the required computation time Tcl. Therefore, according to the configuration of the present invention, it is possible to accurately measure the inter-terminal distance compared to the reference configuration.

[0080] In the present embodiment, the count value of the round trip timer F14 is reset each time the synchronization signal is transmitted. Accordingly, the time from a time T3 to a time T5 shown in Fig. 6 are not mistakenly used as the round-trip time. Note that the pulse signal triggered by the transmission of the synchronization signal at time T3 is not transmitted according to an on-off keying, since the value of the transmission destination bit is 0 at this time.

[0081] When the first terminal and the second terminal perform communication by UWB-IR using on-off gating as in the present embodiment from the start to the end of sending the response data, the second terminal 2 requires time obtained by multiplying a value obtained by subtracting 1 from the bit number n of the response data (ie, n-1) by the transmission interval Tps.

[0082] Therefore, in the configuration in which the first terminal and the second terminal perform communication by means of UWB-IR using on-off gating, the round trip time includes the time obtained by multiplying Tps by n-1 when the time from the completion of sending the data to the completion of receiving the response data in the first terminal (for example, Trt_d in Fig. 7) is used as the orbital time.

[0083] Thus, in order to perform a calculation regarding the inter-terminal distance from the round-trip time obtained by the comparison configuration, it is necessary to exclude from the round-trip time not only the required computing time Tcl but also the time derived from the transmission interval Tps.

[0084] However, the pulse transmission interval itself is influenced by the error of the clock oscillator described above. Therefore, if the bit string being transmitted and received is longer, the error contained in the round-trip time becomes larger.

[0085] Regarding such a problem, according to the configuration of the present embodiment, the element depending on the transmission interval Tps is not included in the round-trip time. Therefore, it is possible to estimate the inter-terminal distance with even higher accuracy.

[0086] When a radio wave is used as a transmission medium for a pulse signal as in the present embodiment, an error of only 7 ns in the round trip time causes an error of 1 m or more to occur in the inter-terminal distance. Therefore, it can be said that determining an even more accurate round trip time is an important task in estimating an accurate inter-terminal distance.

[0087] The first terminal in the above configuration sequentially transmits pulse signals as a synchronization signal at a predetermined transmission interval for a predetermined time after the transmission of the response request signal is completed. Furthermore, the second terminal informs the first terminal of the value of each bit of the response data by sequentially transmitting and not transmitting the pulse signal. Specifically, when the value of the bit as the transmission target has a value (for example, 1) for transmitting the pulse signal, the pulse signal is transmitted, with the reception of the synchronization signal as a trigger.

[0088] Then, the round trip timer arranged in the first terminal measures the time from transmission of the synchronization signal to reception of the pulse signal as the round trip time.

[0089] The round-trip time measured by such a configuration does not include the time required for the second terminal to execute processing to generate response request data corresponding to the response request data (i.e., required computing time). Therefore, the difference between the assumed value of the required computing time and the actual required computing time in the second terminal is not reflected as an error in the runtime.

[0090] Since the round-trip time measured by the above configuration does not include the required computing time in the second terminal, the time measured as the round-trip time itself is shorter than in the assumed configuration described above. As a result, the magnitude of the error resulting from the accuracy of the clock oscillator located in the first terminal and included in the round-trip time to be measured can be reduced.

[0091] According to the above configuration, the round-trip time hardly includes the difference between the assumed value of the required computing time and the actual computing time in the second terminal device, as well as the error resulting from the accuracy of the clock oscillator arranged in the first terminal device. Thus, it is possible to limit the deviation of the round-trip time calculated from the round-trip time from the actual value. That is, it is possible to determine the round-trip time more accurately. As a result, the distance between the first communication terminal device and the second communication terminal device can be estimated more accurately.

[0092] Note that components having the same functions as those described in the above embodiment are denoted by the same reference numerals, and their descriptions are omitted. When referring to only a part of the configuration, the configuration of the above-described embodiment can be used for the other sections. (Application example of the present embodiment)

[0093] The distance estimation system described above can be applied to a known electronic vehicle key system. The electronic vehicle key system is a system that controls the locking state of a vehicle door through wireless communication between a portable device carried by a user and an on-board device mounted in the vehicle. A keyless entry system, a smart entry system, etc., can be used as the electronic vehicle key system.

[0094] For example, the in-vehicle device may function as the first terminal 1, and the portable device may function as the second terminal. In this case, the in-vehicle device may estimate the distance to the portable device by measuring the above round-trip time when performing wireless communication with the portable device.

[0095] The distance estimation system described above can be applied to a system that controls a locking state of a door of a house by means of wireless communication between a portable device carried by a user and a communication device installed in the house.

[0096] When three or more first terminals 1 are arranged at different positions, the position of the second terminal 2 can be determined based on the installation position of each first terminal 1 and the distance from each first terminal 1 to the second terminal 2. That is, the inter-terminal distance estimated by the above embodiment can be used for the position estimation of the second terminal 2. The system for estimating the position of the second terminal 2 can be used for various purposes such as inventory management of goods in distribution and analysis of assembly lines by warehouse workers. (Modification 1)

[0097] In the above-described embodiment, an aspect was described in which the correspondence between the bit pattern of the response request data transmitted by the first terminal 1 and the bit pattern of the response data returned by the second terminal 2 is predetermined, and the second terminal 2 determines the bit pattern of the response data to be returned from the bit pattern of the received response request data. However, this is not limiting. Arithmetic processing using a predetermined function for generating the response data may be included.

[0098] The distance estimation system 100 described above can also be used, for example, for a communication system in which the first terminal 1 and the second terminal 2 perform authentication processing by transmitting and receiving data, for example, a challenge-response method.

[0099] It is assumed that the first terminal 1 arranged in such a communication system transmits data containing a challenge code as response request data to the second terminal 2. The challenge code may be a bit string corresponding to a random sequence or a pre-designed bit string.

[0100] When receiving the data containing the challenge code, the second terminal 2 generates a response code from the challenge code using a predetermined coding function previously registered in the second terminal 2, and returns data containing the response code to the second terminal 2 as response data.

[0101] The first terminal 1 transmits the data containing the challenge code as response request data and generates a verification code from the challenge code using a predetermined coding function. The coding function used here is the same as the coding function registered in the second terminal 2. Then, the response code returned from the second terminal 2 is compared with the verification code, and if these codes match or satisfy a predetermined relationship, it is determined that the authentication is successful. Determining that the authentication is successful corresponds to determining that the communication partner is the second terminal 2.

[0102] Even in such an aspect, the same effect as in the above-described embodiment is achieved because the round trip time measured by the first terminal 1, the calculation time required or the like required for generating the response code is not included. (Further modifications)

[0103] Although an aspect in which the radio wave is transmitted in pulse form as the pulse signal has been described above, the transmitted and received pulse signal may be a sound wave in pulse form.

[0104] Although an aspect in which the first terminal 1 and the second terminal 2 have different functions has been described above, the present invention is not limited to this. The communication terminal arranged in the distance estimation system 100 can have the functions of both the first terminal 1 and the second terminal 2. In other words, the function as the second terminal 2 can be added to the first terminal 1 described above.

[0105] A flowchart or the processing of the flowchart described in the present invention consists of several parts (also referred to as steps), and each part is denoted, for example, by S101. Furthermore, each part can be divided into several sub-parts, while several parts can be combined into one part. Furthermore, each part configured in this way can also be referred to as a circuit, device, module, or device.

[0106] Each of the parts described above, or a combination of the parts, may be not only (i) a software unit combined with a hardware unit (e.g., a computer), but also (ii) hardware (e.g., an integrated circuit, a wiring logic circuit) with or without a function of a relevant device. Furthermore, the hardware section may also be formed within a microcomputer.

[0107] While the invention has been described with reference to specific embodiments, it is to be understood that the invention is not limited to the specific embodiments and constructions. The invention covers various modifications and equivalent arrangements. In addition to the various combinations and configurations, other combinations and configurations including more, fewer, or a single element are also possible within the scope of the invention.

Claims

[1] Distance estimation system that has: a first terminal (1) and a second terminal (2) which perform wireless communication of an on-off keying by transmitting and receiving pulse signals, wherein the first device contains: a data generation unit (F11) that generates response request data for requesting the second terminal to return a response signal, a first terminal-side transmitter (12) which transmits a response request signal in which the pulse signals are arranged at a predetermined transmission interval corresponding to a bit string constituting the response request data, and successively transmits the pulse signals as synchronization signals at the predetermined transmission interval during a predetermined time after the transmission of the response request signal has been terminated, and a first terminal-side receiver (13) which receives the pulse signals returned by the second terminal as the response signal to the response request signal, the second device contains: a second terminal-side receiver (23) which receives the response request signal, a response data generation unit (F22) that generates response data based on a bit string as the response request data determined by demodulating the response request signal received by the second terminal-side receiver, a transmission destination bit setting unit (F23) that shifts a bit that is a transmission destination in a bit string as the response data generated by the response data generation unit by one toward a rear side from a leading bit to a trailing bit each time the synchronization signal is received, and a second terminal-side transmitter (22) which transmits the pulse signal in a case where a value of the bit which is the transmission destination at a time of reception of a synchronization signal is a predetermined value previously determined as a value indicating that the pulse signal is to be transmitted, and does not transmit a pulse signal in a case where the value of the bit is not the predetermined value, and the first device also contains: a round trip timer (F14) which measures a time from a transmission of the synchronization signal to a reception of the pulse signal as a round trip time, and a distance estimation unit (F15) that determines a travel time during which the pulse signal has propagated through a space based on the round trip time measured by the round trip timer, and estimates a distance to the second terminal based on the travel time and a propagation speed, which is a speed at which the pulse signal propagates in the space. [2] The distance estimation system according to claim 1, wherein a count value of the round trip timer is reset each time the synchronization signal is transmitted. [3] Distance estimation system according to claim 1 or 2, wherein the second terminal is designed to transmit a pulse train signal containing the pulse signals as a response signal, the round trip timer measures the round trip time corresponding to each sequence of pulse signals corresponding to the one response signal, and the distance estimation unit estimates the distance to the second terminal using a plurality of round trip times. [4] A distance estimation system according to any one of claims 1 to 3, wherein the pulse signals are a radio wave in pulse form. [5] A distance estimation system according to any one of claims 1 to 3, wherein the pulse signals are a sound wave in pulse form.

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