JP5442343B2 - Wireless device - Google Patents

Description

  The present invention relates to communication technology, and more particularly to a radio apparatus that receives a desired signal in the presence of an interference signal.

  An ITS (Intelligent Transport Systems) inter-vehicle communication system notifies other vehicles of the position, speed information, etc. of the vehicle that is out of sight as one of applications. By this notification, it is expected to prevent an encounter vehicle collision accident at an intersection with poor visibility. The ITS inter-vehicle communication system is scheduled to use the 720 MHz band. The use frequency band of the terrestrial digital television broadcasting system is adjacent to the lower end of the use frequency band of the ITS inter-vehicle communication system with the guard band of 5 MHz interposed therebetween.

  In addition, a frequency band used for telecommunications is adjacent to a high frequency side end portion of a use frequency of the ITS inter-vehicle communication system across a guard band of 5 MHz. As described above, the frequency bands of other systems are adjacent to each other with the guard band between both ends of the frequency band of the ITS vehicle-to-vehicle communication system. There is a possibility of receiving. Under the influence of interference, the reception performance of the ITS inter-vehicle communication system is likely to deteriorate (for example, see Patent Document 1).

JP 2002-271240 A

  When a mobile phone using an adjacent frequency band is brought into a vehicle equipped with a terminal device compatible with the ITS inter-vehicle communication system, the mobile phone may interfere with the terminal device. On the other hand, if the communication quality of the ITS inter-vehicle communication system deteriorates due to interference, the purpose of improving driving safety is not achieved. At this time, it is desirable to simply notify the driver of the generation of an interference signal and a reduction method using the interference signal.

  The present invention has been made in view of such a situation, and an object thereof is to provide a technique for easily notifying a user of the occurrence of an interference signal.

  In order to solve the above-described problem, a wireless device according to an aspect of the present invention is a wireless device mounted on a vehicle, and includes an acquisition unit that acquires information related to the location of the vehicle, and information acquired by the acquisition unit. A communication unit that transmits a received packet signal and receives a packet signal from a wireless device mounted on another vehicle, and an extraction that extracts information on the location of the other vehicle from the packet signal received by the communication unit Based on the information extracted by the extraction unit, a notification unit for notifying the presence position of another vehicle, and an estimation unit for estimating the presence of an interference signal with respect to the packet signal received by the communication unit. The notification unit also notifies the presence of the interference signal when the estimation unit estimates the presence of the interference signal.

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

  According to the present invention, it is possible to easily notify the user of the occurrence of an interference signal.

It is a figure which shows the structure of the communication system which concerns on the Example of this invention. It is a figure which shows the channel arrangement | positioning of the communication system of FIG. It is a figure which shows the structure of the terminal device mounted in the vehicle of FIG. 4A to 4D are diagrams illustrating an outline of processing in the detection unit of FIG. It is a figure which shows the image displayed in the notification part of FIG. It is a flowchart which shows the procedure of the reception process by the terminal device of FIG. It is a flowchart which shows the procedure of the detection process by the terminal device of FIG. It is a flowchart which shows the procedure of the detection process by the terminal device which concerns on the modification of this invention. It is a figure which shows the structure of the terminal device which concerns on another modification of this invention. It is a figure which shows the outline | summary of the process in the detection part of FIG. It is a figure which shows the image displayed in the notification part of FIG. It is a figure which shows the structure of the terminal device which concerns on another modification of this invention. It is a figure which shows the image displayed in the notification part of FIG.

  Before describing the present invention in detail, an outline will be described. An embodiment of the present invention relates to a communication system that performs data communication between terminal devices mounted on a vehicle. The terminal device transmits a packet signal storing information such as the speed and position of the vehicle (hereinafter referred to as “data”) (hereinafter, the packet signal storing the data may be referred to as “data”). On the other hand, the terminal device receives a packet signal transmitted from another terminal device and recognizes the approach of another vehicle on which the other terminal device is mounted based on the data. Here, it is assumed that broadcast transmission is performed as transmission in order to efficiently receive data to a plurality of terminal devices. Further, a band for a terrestrial digital television broadcasting system is arranged adjacent to a low frequency side of a band for a communication system, and a band for a mobile phone system is arranged on a high frequency side of the band for a communication system. Bands are arranged adjacent to each other.

  Communication quality of a communication system is affected by interference waves from a terrestrial digital television broadcasting system and a mobile phone system. Therefore, it is effective for the driver to grasp the influence of interference in advance. For example, when the influence of the interference by the mobile phone system is large, the driver can perform a treatment such that the mobile phone device in the vehicle is separated from the terminal device. It is preferable that the period required for grasping the influence of such interference is shorter. On the other hand, when the communication system supports the OFDM modulation scheme, demodulation is started after the FFT window is appropriately set. As described above, depending on the radio wave environment, it may be difficult to set the FFT window appropriately. Even in such a case, the processing for grasping the influence of interference is required to be executed. In order to cope with this, the communication system according to the present embodiment executes the following processing.

  The terminal device according to the embodiment generates a frequency domain signal by performing FFT even before the FFT window is appropriately set. Further, the terminal device derives a power distribution in the frequency domain by measuring the reception power of each subcarrier signal included in the frequency domain signal. Further, the terminal device derives the slope of the received power in the frequency direction from the power distribution. If the absolute value of the slope is larger than the threshold value, the terminal apparatus estimates that an interference wave exists on the frequency side with the larger received power. Further, the terminal device executes the same processing even after the FFT window is appropriately set. That is, the terminal device can estimate the presence of an interference wave regardless of whether or not the FFT window is appropriately set. Further, the terminal device notifies the driver of the presence of the interference wave.

  FIG. 1 shows a configuration of a communication system 100 according to an embodiment of the present invention. This corresponds to a case where one intersection is viewed from above. The communication system 100 includes a first vehicle 12a, a second vehicle 12b, a third vehicle 12c, a fourth vehicle 12d, a fifth vehicle 12e, a sixth vehicle 12f, a seventh vehicle 12g, and an eighth vehicle 12h, which are collectively referred to as a vehicle 12. including. Each vehicle 12 is equipped with a terminal device (not shown).

  As shown in the drawing, the road that goes in the horizontal direction of the drawing, that is, the left and right direction, intersects the vertical direction of the drawing, that is, the road that goes in the up and down direction, at the central portion. Here, the upper side of the drawing corresponds to the direction “north”, the left side corresponds to the direction “west”, the lower side corresponds to the direction “south”, and the right side corresponds to the direction “east”. The intersection of the two roads is an “intersection”. The first vehicle 12a and the second vehicle 12b are traveling from left to right, and the third vehicle 12c and the fourth vehicle 12d are traveling from right to left. Further, the fifth vehicle 12e and the sixth vehicle 12f are traveling from the top to the bottom, and the seventh vehicle 12g and the eighth vehicle 12h are traveling from the bottom to the top.

  The terminal device mounted on each vehicle 12 acquires data and broadcasts a packet signal in which the data is stored. Here, each terminal device corresponds to CSMA / CA (Carrier Sense Multiple Access Collision Aviation) as in a known wireless LAN (Local Area Network), and is determined to be capable of performing carrier sense and transmitting. If this happens, broadcast data. As described above, the band used by the terrestrial digital television broadcasting system (not shown) and the band used by the mobile phone system are arranged around the band used by the communication system 100. Since the influence of interference from other systems affects the communication quality, each terminal apparatus estimates the influence of interference from other systems. The estimation of the influence of interference will be described later.

  FIG. 2 shows a channel arrangement of the communication system 100. The horizontal axis represents frequency and the vertical axis represents power. As illustrated, the communication system 100 is disposed in a communication system band 114. Further, the first guard band 112 is arranged adjacent to the low frequency side of the communication system band 114, and the terrestrial digital broadcast band 110 is arranged adjacent to the low frequency side of the first guard band 112. . The terrestrial digital broadcast band 110 is used by the terrestrial digital broadcast 102. A part of the spectrum of the terrestrial digital broadcast 102 extends to the communication system band 114 as shown in the figure. Usually, this part of power is set so as not to affect the communication system 100, but depending on the radio wave environment of the communication system 100 and the terrestrial digital broadcast 102, part of the power of the terrestrial digital broadcast 102 is used. May affect the communication system 100.

  Further, the second guard band 116 is disposed adjacent to the high frequency side of the communication system band 114, and the mobile phone system band 118 is disposed adjacent to the high frequency side of the second guard band 116. The cellular phone system band 118 is used by the cellular phone system 104. A part of the spectrum of the mobile phone system 104 covers the communication system band 114 as shown in the figure. The influence of part of the power of the mobile phone system 104 on the communication system 100 is the same as in the case of the terrestrial digital broadcast 102.

  FIG. 3 shows a configuration of the terminal device 14 mounted on the vehicle 12. The terminal device 14 includes an antenna 20, a radio unit 22, a transmission unit 24, a reception unit 26, and a control unit 28. The transmission unit 24 includes an acquisition unit 30, a generation unit 32, a modulation unit 34, and an IFFT unit 36. The receiving unit 26 includes a synchronization unit 38, a setting unit 40, an FFT unit 42, a demodulation unit 44, a notification unit 46, a detection unit 48, and an estimation unit 50. Further, the detection unit 48 includes a measurement unit 52, a moving average unit 54, a derivation unit 56, and a comparison unit 58.

  The acquisition unit 30 includes a GPS receiver, a gyroscope, a vehicle speed sensor, and the like, and acquires the location of the vehicle 12 on which the terminal device 14 is mounted, the traveling direction of the vehicle, the moving speed, and the like. The existence position is indicated by latitude and longitude. Since a well-known technique should just be used for acquisition of an existing position etc. by the acquisition part 30, description is abbreviate | omitted here. The acquisition unit 30 outputs information related to the location of the vehicle 12, that is, the above-described data to the generation unit 32.

  The generation unit 32 acquires data from the acquisition unit 30. The generation unit 32 generates a packet signal so as to store data. The packet signal also includes information for identifying the terminal device 14. The generation unit 32 outputs the generated packet signal to the modulation unit 34. The modulation unit 34 modulates the packet signal from the generation unit 32. As a modulation method, BPSK, QPSK, 16QAM, 64QAM and the like are defined. Also, the modulation unit 34 outputs the modulated result to the IFFT unit 36 as a baseband packet signal. Note that the baseband packet signal corresponds to an OFDM signal in the frequency domain. In general, baseband packet signals are formed by in-phase and quadrature components, so two signal lines should be shown, but here only one signal line is shown for clarity. Shall be shown.

  The IFFT unit 36 receives a baseband packet signal from the modulation unit 34. The IFFT unit 36 performs an IFFT (Inverse Fast Fourier Transform) to convert an OFDM signal in the frequency domain into an OFDM signal in the time domain. A time-domain OFDM signal is also referred to as a baseband packet signal. As a transmission process, the radio unit 22 performs frequency conversion on the baseband packet signal input from the IFFT unit 36 to generate a radio frequency packet signal. Further, the radio unit 22 broadcasts a radio frequency packet signal from the antenna 20. The wireless unit 22 includes a PA (Power Amplifier), a mixer, and a D / A conversion unit. As described above, the packet signal is transmitted in accordance with an access control function called CSMA / CA, similarly to a wireless LAN compliant with a standard such as IEEE 802.11.

  As a reception process, the radio unit 22 receives a packet signal notified from another terminal device 14 (not shown) by the antenna 20. The other terminal device 14 is mounted on another vehicle 12 (not shown). The radio unit 22 performs frequency conversion on a radio frequency packet signal received via the antenna 20 to generate a baseband packet signal. Here, the baseband packet signal is an OFDM signal in the time domain. Further, the radio unit 22 outputs a baseband packet signal to the receiving unit 26. The wireless unit 22 also includes an LNA (Low Noise Amplifier), a mixer, an AGC, and an A / D conversion unit.

  The synchronization unit 38 inputs the time-domain OFDM signal received by the radio unit 22. The synchronization unit 38 detects a synchronization timing when the FFT unit 42 described later converts the time domain OFDM signal into the frequency domain OFDM signal based on the time domain OFDM signal. Here, the synchronization timing corresponds to a window timing for executing FFT. For detecting the synchronization timing, a known technique may be used. For example, autocorrelation processing or cross-correlation processing is performed. The synchronization unit 38 detects the peak of the correlation value as the synchronization timing. When executing the cross-correlation process, the synchronization unit 38 stores a known signal pattern in advance. The synchronization unit 38 notifies the setting unit 40 of the synchronization timing. The synchronization timing is detected for each packet signal.

  The setting unit 40 receives the synchronization timing from the synchronization unit 38 when the synchronization unit 38 detects the synchronization timing. The setting unit 40 sets the synchronization timing in the FFT unit 42. The FFT unit 42 inputs the time-domain OFDM signal input by the receiving unit 26. When the setting unit 40 sets the synchronization timing, the FFT unit 42 performs FFT at the window timing corresponding to the synchronization timing. As a result, the FFT unit 42 converts the time domain OFDM signal into a frequency domain OFDM signal. The frequency domain OFDM signal is formed by a plurality of subcarrier signals. The FFT unit 42 performs FFT based on an arbitrary timing when the synchronization timing is not set by the setting unit 40. Regardless of when the synchronization timing is set or when the synchronization timing is not set, the FFT unit 42 outputs the frequency domain OFDM signal to the detection unit 48. When the synchronization timing is set, the FFT unit 42 outputs the frequency domain OFDM signal to the demodulation unit 44.

  The demodulator 44 receives the frequency domain OFDM signal from the FFT unit 42 when the setting unit 40 sets the synchronization timing in the FFT unit 42. The demodulator 44 demodulates the frequency domain OFDM signal. As described above, since the OFDM signal in the frequency domain is formed by a plurality of subcarrier signals, the demodulation unit 44 performs a demodulation process on each of the plurality of subcarrier signals. The demodulation unit 44 outputs the demodulated result to the notification unit 46.

  The notification unit 46 receives the demodulation result from the demodulation unit 44. The notification unit 46 processes the demodulation result to obtain information on the location of other vehicles included in the packet signal. The notification unit 46 detects the presence position, approach, and the like of the other vehicle 12 based on information regarding the presence position of the other vehicle. At that time, the notification unit 46 may receive information on the location of the host vehicle from the acquisition unit 30. Further, the notification unit 46 notifies the driver of an approach or the like via a monitor or a speaker (not shown). A collision accident is prevented when the driver recognizes the approach of another vehicle. When notifying the approach of another vehicle on the monitor, the notification unit 46 may synthesize an image of the other vehicle on the map image displayed by the car navigation device.

  The measurement unit 52 receives the OFDM signal in the frequency domain converted by the FFT unit 42 regardless of whether the synchronization timing is set by the setting unit 40. Measurement unit 52 measures received power for each of a plurality of subcarrier signals forming an OFDM signal in the frequency domain. Measurement unit 52 may average received power for each of the plurality of subcarrier signals over a predetermined period. Measurement unit 52 outputs received power for each of the plurality of subcarrier signals to moving average unit 54.

  The moving average unit 54 receives the received power for each of the plurality of subcarrier signals from the measurement unit 52. The moving average unit 54 derives a moving average value in the frequency domain for the received power of the plurality of subcarrier signals. More specifically, the moving average unit 54 sets windows corresponding to ten consecutive subcarrier signals, and averages received power included in the windows. The moving average unit 54 derives an average value corresponding to each subcarrier signal by moving the window from the low frequency side to the high frequency side of the communication system band 114 of FIG. Each of these average values corresponds to a moving average value. The moving average unit 54 outputs each moving average value to the derivation unit 56.

  The deriving unit 56 receives a plurality of moving average values from the moving average unit 54. Each of the plurality of moving average values is associated with a frequency in the communication system band 114. The deriving unit 56 derives the slope of the received power from the low frequency side to the high frequency side of the OFDM signal in the frequency domain based on the moving average value. Specifically, the deriving unit 56 extracts a moving average value corresponding to a point on the low frequency side of the communication system band 114 (hereinafter referred to as “low frequency side moving average value”). The deriving unit 56 also extracts a moving average value corresponding to one point on the high frequency side (hereinafter referred to as “high frequency side moving average value”). Furthermore, the deriving unit 56 derives a slope from the low frequency side moving average value to the high frequency side moving average value. That is, the deriving unit 56 derives the slope based on a predetermined number of subcarrier signals among a plurality of subcarrier signals forming the frequency domain OFDM signal. Note that the slope may be derived by processing other than this, for example, by using the least square method. The derivation unit 56 outputs the inclination to the comparison unit 58.

  The comparison unit 58 receives the inclination from the derivation unit 56. In addition, the comparison unit 58 stores a threshold value for the inclination. The comparison unit 58 derives the absolute value of the slope, and when the absolute value of the slope is larger than the threshold, the received power of the frequency domain OFDM signal is changed from one frequency side to the other in the frequency domain OFDM signal. It is detected that there is an upward trend toward the frequency side. The comparison unit 58 accepts both the low frequency side moving average value and the high frequency side moving average value from the derivation unit 56, and when the high frequency side moving average value is larger than the low frequency side moving average value, One frequency side described above corresponds to the low frequency side, and the other frequency side corresponds to the high frequency side. Further, when the moving average value on the low frequency side is larger than the moving average value on the high frequency side, the one frequency side described above corresponds to the high frequency side, and the other frequency side corresponds to the low frequency side. On the other hand, when the absolute value of the slope is not larger than the threshold value, the comparison unit 58 detects that the OFDM signal in the frequency domain does not have an upward tendency. When the comparison unit 58 has an upward tendency, the comparison unit 58 outputs the fact and information on the frequency having the larger moving average value to the estimation unit 50.

  4A to 4D show an outline of processing of the detection unit 48. FIG. 4A to 4D, the horizontal axis indicates the frequency, and the vertical axis indicates the power. FIG. 4A shows received power for each of a plurality of subcarrier signals measured by the measurement unit 52. FIG. 4B shows the moving average value derived by the moving average unit 54. Here, the above-mentioned “one point on the low frequency side” is indicated as “f1”, and “one point on the high frequency side” is indicated as “f2”. Further, the above-mentioned “low frequency side moving average value” is indicated as “P1”, and “high frequency side moving average value” is indicated as “P2”. FIG. 4C shows the moving average value as in FIG. 4B, but corresponds to the case where the absolute value of the slope is large. Here, the case where the high frequency side moving average value is larger than the low frequency side moving average value is shown. FIG. 4D shows the moving average value when the absolute value of the slope is large, as in FIG. FIG. 4D shows a case where the low frequency side moving average value is larger than the high frequency side moving average value, unlike FIG. 4C. Returning to FIG.

  When the detecting unit 48 detects an upward tendency, the estimating unit 50 receives that fact and information on the frequency having the larger moving average value. Upon receiving these, the estimation unit 50 estimates the presence of interference power on the frequency side with the larger moving average value. For example, if the moving average value on the low frequency side is larger, the presence of the interference signal on the low frequency side is estimated, and if the moving average value on the high frequency side is larger, the presence of the interference signal on the high frequency side is estimated. . According to FIG. 2, the interference signal on the low frequency side corresponds to the interference signal from the terrestrial digital broadcast 102, and the interference signal on the high frequency side corresponds to the interference signal from the mobile phone system 104. The estimation unit 50 outputs the estimation result to the notification unit 46.

  The notification unit 46 also notifies the presence of the interference signal when the estimation unit 50 estimates the presence of the interference signal. More specifically, the notification unit 46 notifies the driver that there is interference from the terrestrial digital broadcast 102 when the presence of an interference signal on the low frequency side is estimated. On the other hand, when the presence of an interference signal on the high frequency side is estimated, the notification unit 46 notifies the driver that there is interference by the mobile phone system 104. FIG. 5 shows an image displayed on the notification unit 46. This is an image when there is interference by the mobile phone system 104. As shown in the figure, when a mobile phone is present in the vehicle 12, the fact that the communication quality of the communication system 100 is improved is notified by turning off the power of the mobile phone. Returning to FIG. At that time, the driver can reduce interference with the communication system 100 by turning off the power of the mobile phone. Note that the detection unit 48 and the estimation unit 50 execute the processing regardless of whether the synchronization timing is set by the setting unit 40. The control unit 28 controls the timing of the entire terminal device 14.

  This configuration can be realized in terms of hardware by a CPU, memory, or other LSI of any computer, and in terms of software, it can be realized by a program loaded in the memory, but here it is realized by their cooperation. Draw functional blocks. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  The operation of the terminal device 14 configured as above will be described. FIG. 6 is a flowchart illustrating a procedure of reception processing by the terminal device 14. When the timing synchronization is not established in the synchronization unit 38 (N in S10), the FFT unit 42 executes FFT at an arbitrary window timing (S12). The detection unit 48 performs detection processing based on the OFDM signal subjected to the FFT (S14). On the other hand, when the timing synchronization is established in the synchronization unit 38 (Y in S10), the FFT unit 42 executes the FFT at the synchronized window timing (S16). The demodulator 44 performs demodulation processing on the FFTed OFDM signal (S18). The detection unit 48 performs detection processing based on the OFDM signal subjected to the FFT (S20).

  FIG. 7 is a flowchart illustrating the procedure of the detection process performed by the terminal device 14. The measuring unit 52 measures received power (S40). The moving average unit 54 calculates a moving average with respect to the received power (S42). When P1 is larger than P2 (Y in S44), if the absolute value of the slope is larger than the threshold value (Y in S46), the estimation unit 50 estimates that interference from the terrestrial digital broadcast 102 has occurred. (S48). If the absolute value of the slope is not greater than the threshold value (N in S46), the process is terminated. When P1 is not larger than P2 (N in S44), if the absolute value of the slope is larger than the threshold value (Y in S50), the estimation unit 50 estimates that interference by the mobile phone system 104 has occurred. (S52). If the absolute value of the slope is not greater than the threshold value (N in S50), the process is terminated.

  Next, a modified example of the present invention will be described. The modification of this invention is related with the communication system which performs data communication between the terminal devices mounted in the vehicle similarly to the Example. Further, the terminal device according to the modified example estimates the presence of an interference signal based on the slope of the received power, as in the embodiment. In the embodiment, after the received power for each of the plurality of subcarrier signals is measured, the slope is derived based on some of the values. That is, in the embodiment, selection is made following the measurement. On the other hand, in the modification, a subcarrier signal to be used for measurement is selected in advance from among a plurality of subcarrier signals, and the received power is measured for the selected subcarrier signal. Thereafter, the slope is derived. That is, in the modification, measurement is performed following selection. The communication system 100 and the terminal device 14 according to the modification are the same type as those in FIGS. Therefore, here, the difference will be mainly described.

  The measurement unit 52 selects a low-frequency side subcarrier signal and a high-frequency side subcarrier signal from among the plurality of subcarrier signals forming the frequency domain OFDM signal converted by the FFT unit 42. . The selected subcarrier signal may be determined in advance. Measurement unit 52 measures the received power for the selected subcarrier signal. The measurement unit 52 may average the received power for the subcarrier signal over a predetermined period. The measuring unit 52 outputs received power to the deriving unit 56. The deriving unit 56 regards the received power for the low-frequency side subcarrier signal as the low-frequency side moving average value, regards the received power for the high-frequency side subcarrier signal as the high-frequency side moving average value, and executes the above-described processing. To do. In that case, the moving average part 54 becomes unnecessary.

  On the other hand, the measurement unit 52 may select two or more subcarrier signals as low frequency side subcarrier signals, and may select two or more subcarrier signals as high frequency side subcarrier signals. At that time, the measurement unit 52 measures received power for all the selected subcarrier signals. The moving average unit 54 averages received power for two or more subcarrier signals selected as low frequency side subcarrier signals. The averaged result is called the low frequency side average value. The moving average unit 54 also averages received power for two or more subcarrier signals selected as high frequency side subcarrier signals. The averaged result is called the high frequency side average value. The moving average unit 54 outputs the low frequency side average value and the high frequency side average value to the derivation unit 56. The deriving unit 56 regards the low frequency side average value as the low frequency side moving average value, regards the high frequency side average value as the high frequency side moving average value, and executes the above-described processing.

  FIG. 8 is a flowchart showing a procedure of detection processing by the terminal device 14 according to the modification of the present invention. The measuring unit 52 selects two points (S70) and measures received power (S72). When P1 is larger than P2 (Y in S74), if the absolute value of the slope is larger than the threshold value (Y in S76), the estimation unit 50 estimates that interference from the terrestrial digital broadcast 102 has occurred. (S78). If the absolute value of the slope is not greater than the threshold value (N in S76), the process is terminated. When P1 is not larger than P2 (N in S74), if the absolute value of the slope is larger than the threshold value (Y in S80), the estimation unit 50 estimates that interference by the mobile phone system 104 has occurred. (S82). If the absolute value of the slope is not greater than the threshold value (N in S80), the process is terminated.

  Next, another modification of the present invention will be described. Another modification of the present invention also relates to a communication system that performs data communication between terminal devices mounted on a vehicle, as before. The terminal device also estimates the presence of an interference signal from a mobile phone system or the like, and prompts the driver to turn off the mobile phone. A terminal apparatus according to another modification includes a plurality of antennas, and performs interference signal estimation processing on packet signals received by each of the plurality of antennas. Further, the communication status for each of the plurality of antennas is notified to the driver. A communication system 100 according to another modification is the same type as that in FIG.

  FIG. 9 shows a configuration of a terminal device 14 according to another modification of the present invention. The terminal device 14 includes a first antenna 20a, a second antenna 20b, which are collectively referred to as an antenna 20, a first radio unit 22a, a second radio unit 22b, which are collectively referred to as a radio unit 22, a transmission unit 24, a reception unit 26, and a control unit. 28. The transmission unit 24 includes an acquisition unit 30, a generation unit 32, a transmission diversity unit 70, a first modulation unit 34a collectively referred to as a modulation unit 34, a second modulation unit 34b, a first IFFT unit 36a collectively referred to as an IFFT unit 36, a first 2 IFFT part 36b is included. The receiving unit 26 includes a first FFT unit 42a, a second FFT unit 42b, which are collectively referred to as an FFT unit 42, a first demodulation unit 44a, a second demodulation unit 44b, which is collectively referred to as a demodulation unit 44, a reception diversity unit 72, a notification unit 46, A first detection unit 48a, a second detection unit 48b, and an estimation unit 50, which are collectively referred to as the detection unit 48, are included. In FIG. 9, the synchronization unit 38 and the setting unit 40 are omitted. Here, among the constituent elements shown in FIG. 9 and the constituent elements shown in FIG. 3, the same reference numerals are given to the constituent elements corresponding to each other, and the difference from FIG. 3 will be mainly described. To do.

  The transmission diversity unit 70 receives the packet signal from the generation unit 32 and outputs the packet signal to the first modulation unit 34a or the second modulation unit 34b. For example, the transmission diversity unit 70 switches the output destination for each packet signal so that the packet signal is output to the first modulation unit 34a and the next packet signal is output to the second modulation unit 34b at a predetermined timing. Further, the transmission diversity unit 70 may select one output destination over a predetermined period. Furthermore, since the packet signal is a frequency domain packet signal, the transmission diversity unit 70 may select the first modulation unit 34a or the second modulation unit 34b in units of subcarrier signals. The first modulation unit 34a, the first IFFT unit 36a, the first radio unit 22a, and the first antenna 20a perform transmission processing similar to that in the embodiment. The same applies to the second modulation unit 34b, the second IFFT unit 36b, the second radio unit 22b, and the second antenna 20b.

  The first antenna 20a, the first radio unit 22a, the first FFT unit 42a, and the first demodulation unit 44a execute the same reception process as in the embodiment. The same applies to the second antenna 20b, the second radio unit 22b, the second FFT unit 42b, and the second demodulation unit 44b. Therefore, the FFT unit 42 converts the time domain OFDM signal received by each of the plurality of antennas 20 into a frequency domain OFDM signal. The reception diversity unit 72 receives the demodulation result from the first demodulation unit 44a and the demodulation result from the second demodulation unit 44b, and executes reception diversity. A known technique may be used as the reception diversity. For example, selection diversity is performed. When equal gain combining diversity or maximum ratio combining diversity is performed as the reception diversity, the reception diversity unit 72 may be provided before the demodulation unit 44.

  The first detection unit 48a performs the same processing as the embodiment on the frequency domain OFDM signal from the first FFT unit 42a, and the second detection unit 48b performs the frequency domain OFDM signal from the second FFT unit 42b. In contrast, the same processing as in the embodiment is executed. As a result, the first detection unit 48a and the second detection unit 48b indicate that the reception power of the OFDM signal in the frequency domain has a tendency to increase from one frequency side to the other frequency side in the frequency domain. Detect each. The first detection unit 48a and the second detection unit 48b execute such detection processing independently of each other. FIG. 10 shows an outline of the processing of the detection unit 48. FIG. 10 is shown similarly to FIGS. 4 (a)-(d). In FIG. 10, the solid line corresponds to the OFDM signal from the first FFT unit 42a, and the dotted line corresponds to the OFDM signal from the second FFT unit 42b. Here, it is assumed that an upward trend is detected by the second detection unit 48b and no upward trend is detected by the first detection unit 48a. Returning to FIG.

  The estimation unit 50 estimates the presence of an interference signal when it is detected that one of the first detection unit 48a and the second detection unit 48b has an upward tendency. When the estimation unit 50 estimates the presence of the interference signal, the estimation unit 50 outputs the fact to the notification unit 46. When the notification unit 46 receives the notification from the estimation unit 50, the notification unit 46 notifies the driver of the presence of the interference signal as in the embodiment. Note that the notification unit 46 may notify the communication status of each antenna 20. FIG. 11 shows an image displayed on the notification unit 46. As illustrated, the communication status for each antenna 20 is displayed as the number of antennas. The notification unit 46 receives the inclination value from each detection unit 48, and determines the number of antennas from the inclination value based on a relationship such that the larger the inclination value, the smaller the number of antennas.

  Next, still another modification of the present invention will be described. Still another modified example of the present invention relates to a communication system that performs data communication between terminal devices mounted on a vehicle, as before. Further, the terminal device includes a plurality of antennas, estimates the presence of an interference signal from a mobile phone system or the like, and prompts the driver to turn off the mobile phone. Until now, the presence of an interference signal has been estimated based on the shape of the OFDM signal in the frequency domain. On the other hand, a terminal apparatus according to still another modification performs adaptive array signal processing, and estimates the direction of the interference signal based on the shape of the beam formed by the weight vector. A communication system 100 according to another modification is the same type as that shown in FIG.

  FIG. 12 shows a configuration of a terminal device 14 according to still another modified example of the present invention. The terminal device 14 includes a first antenna 20 a and a second antenna 20 b that are collectively referred to as an antenna 20, a first radio unit 22 a and a second radio unit 22 b that are collectively referred to as a radio unit 22, a reception unit 26, and a control unit 28. The receiving unit 26 includes a first FFT unit 42 a, a second FFT unit 42 b, an array combining unit 80, a demodulation unit 44, a notification unit 46, a detection unit 48, and an estimation unit 50, which are collectively referred to as the FFT unit 42. In FIG. 12, the transmission unit 24, the synchronization unit 38, and the setting unit 40 shown in FIG. 3 and FIG. 9 are omitted. Here, among the components shown in FIG. 12 and the components shown in FIGS. 3 and 9, the same reference numerals are given to the components corresponding to each other, and FIGS. The difference will be mainly described.

  The array synthesizing unit 80 receives the frequency domain OFDM signal (hereinafter referred to as “first OFDM signal”) from the first FFT unit 42a, and the frequency domain OFDM signal (hereinafter referred to as “second OFDM signal”) from the second FFT unit 42b. Also accept). The array synthesis unit 80 performs adaptive array signal processing on the first OFDM signal and the second OFDM signal. Since a known technique may be used for adaptive array signal processing, description thereof is omitted here. Note that the result of array synthesis is also an OFDM signal in the frequency domain, and the array synthesis unit 80 outputs the result of array synthesis to the demodulation unit 44.

ここで、Ｖ（θ）は、次のように示される。

検出部４８は、θを変化させながらＤの値を計算し、Ｄの値が小さい場合のθがヌルの方向に相当する。 The detection unit 48 receives a weight vector from the array synthesis unit 80. The detection unit 48 calculates the beam directivity based on the weight vector, and specifies the null direction. Specifically, when the weight vector is W, the power directivity function D (θ) is expressed as follows.

Here, V (θ) is expressed as follows.

The detection unit 48 calculates the value of D while changing θ, and θ when the value of D is small corresponds to the null direction.

  The estimation unit 50 receives the null direction from the detection unit 48. Moreover, the estimation part 50 estimates that an interference signal exists in the null direction. That is, the estimation unit 50 estimates the presence of an interference signal based on the weight vector in adaptive array signal processing. When the interference signal exists, the estimation unit 50 outputs a null direction to the notification unit 46 as the direction of the interference signal. When the notification unit 46 receives the notification from the estimation unit 50, the notification unit 46 notifies the driver of the presence of the interference signal as in the embodiment. At that time, the notification unit 46 may notify the direction of the interference signal. FIG. 13 shows an image displayed on the notification unit 46. Here, the case where the interference signal from the front of the vehicle 12 exists is shown. As shown in the figure, it is indicated that it is difficult to receive a signal from the front. Note that the notification unit 46 prepares a plurality of images according to the direction of the interference signal, and selects one image according to the notification from the estimation unit 50.

  According to the embodiment of the present invention, in the frequency domain OFDM signal, the presence of an interference signal is detected by detecting whether or not the received power tends to increase from one frequency side to the other frequency side. Since the estimation is performed, the detection process can be executed regardless of whether timing synchronization is established. Further, since the detection process is executed regardless of whether timing synchronization is established, the influence of interference can be grasped. Even if timing synchronization is not established, the presence of interference can be grasped, so that early grasping can be realized. Moreover, since an early grasp is implement | achieved, the deterioration of quality can be suppressed. In addition, the detection process is the same regardless of whether timing synchronization is established, so that the switching process can be eliminated. In addition, since the switching process is unnecessary, the process can be simplified.

  Further, since the rising tendency is detected by comparing the received power with the threshold value, the processing can be simplified. Further, when the synchronization timing is detected, demodulation processing is executed, so that desired data can be acquired. In addition, since the detection process is performed while performing the demodulation process, the influence of the latest interference can be grasped. Further, since the detection process is executed for a predetermined number of subcarrier signals among the plurality of subcarrier signals, the processing amount can be reduced. Moreover, since moving average is performed with respect to received power, the influence of noise can be reduced. In addition, since the influence of noise is reduced, the processing accuracy can be improved. Further, since the received power is measured only for the selected subcarrier signal, the processing amount can be reduced.

  In addition, since the driver is notified when an interference signal is detected, it is possible to prompt the mobile phone to be turned off. Further, since the power-off of the mobile phone is urged, the communication quality can be improved. Further, since communication quality is improved, it is possible to accurately notify the driver of the approach of another vehicle. In addition, since the driver is accurately notified of the approach of another vehicle, the occurrence of a traffic accident can be suppressed. In addition, since the presence of an interference signal is estimated for each of a plurality of antennas, and the presence of the interference signal is notified when any of them exists, the detection probability of the interference signal can be improved. Moreover, since the detection probability of the interference signal is improved, it is possible to promptly turn off the power of the mobile phone. In addition, since the presence status of the interference signal for each antenna is notified, the communication status for each antenna can be notified. Moreover, since adaptive array signal processing is performed, communication quality can be improved. In addition, since the direction in which the interference signal exists is estimated based on the weight vector in adaptive array signal processing, detailed information can be notified to the driver. Moreover, since detailed information is notified to the driver, the driver can be made to understand the communication status in detail.

  In the above, this invention was demonstrated based on the Example. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. .

  In the embodiment of the present invention, the detector 48 detects an interference signal based on the received power for each subcarrier signal. However, regardless of this, for example, the detection unit 48 may derive an EVM (Error Vector Magnitude) for each subcarrier signal and detect an interference signal based on the EVM for each subcarrier signal. Since the processing of the detection unit 48 at that time only needs to change the received power so far to EVM, description thereof is omitted here. According to this modification, the influence of distortion is reflected by using the EVM, and the interference signal can be accurately detected.

  In the embodiment of the present invention, the detector 48 detects an interference signal based on the received power for each subcarrier signal. However, the present invention is not limited to this. For example, when a null subcarrier is arranged in an OFDM signal in the frequency domain, the presence of an interference signal may be detected based on the received power in the null subcarrier. If a null subcarrier is arranged on the high frequency side of the OFDM signal in the frequency domain, if the received power on the subcarrier is larger than the threshold value, the detection unit 48 detects the interference signal on the high frequency side. Detect presence. In this case, the process for deriving the inclination is omitted. According to this modification, the process for detecting the presence of an interference signal can be simplified.

  12 vehicle, 14 terminal device, 20 antenna, 22 radio unit, 24 transmission unit, 26 reception unit, 28 control unit, 30 acquisition unit, 32 generation unit, 34 modulation unit, 36 IFFT unit, 38 synchronization unit, 40 setting unit, 42 FFT unit, 44 demodulation unit, 46 notification unit, 48 detection unit, 50 estimation unit, 52 measurement unit, 54 moving average unit, 56 derivation unit, 58 comparison unit, 100 communication system.

Claims (3)

A wireless device mounted on a vehicle,
An acquisition unit for acquiring information related to the location of the vehicle;
A communication unit that transmits a packet signal including information acquired in the acquisition unit and receives a packet signal from a wireless device mounted on another vehicle;
An extraction unit that extracts information on the location of other vehicles from the packet signal received in the communication unit;
Based on the information extracted in the extraction unit, a notification unit for notifying the location of other vehicles;
An estimation unit that estimates the presence of an interference signal with respect to a packet signal received by the communication unit;
The communication unit receives a time domain signal as a packet signal, and then converts the time domain signal into a frequency domain signal,
When the estimation unit detects that the received power of the frequency domain signal converted in the communication unit has a rising tendency from one frequency side of the frequency domain signal to the other frequency side, A radio apparatus that estimates the presence of an interference signal on the other frequency side. The communication unit receives a time domain signal in each of a plurality of antennas, and then converts each time domain signal into a frequency domain signal,
2. The radio according to claim 1, wherein the estimation unit estimates the presence of an interference signal when detecting that any one of a plurality of frequency domain signals has a rising tendency. apparatus. The communication unit performs adaptive array signal processing on packet signals received at each of a plurality of antennas,
The radio apparatus according to claim 1, wherein the estimation unit estimates the presence of an interference signal based on a weight vector in adaptive array signal processing.

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