Receiving device and receiving method

Abstract

The present invention provides a receiving device and a receiving method that can improve the receiving performance of receiving radio waves transmitted by a transmitter, even when the receiving antenna cannot be positioned away from a noise source. [Solution] The first receiving antenna 18 and the second receiving antenna 19, which receive the transmitted radio waves Sa transmitted from the transmitter 3, are positioned along the propagation path of the transmitted radio waves Sa which are diffracted by the radio wave shielding provided on the vehicle 2, at a position where they receive noise waves transmitted from the noise source of the vehicle 2 in phase, and at positions spaced apart d from each other. The conversion unit 15 converts the phase of the first received radio wave Sb1 received by the first receiving antenna 18 to the phase of the second received radio wave Sb2 received by the second receiving antenna 19. The combiner 16 combines the first received radio wave Sb1 input from the conversion unit 15 and the second received radio wave Sb2 received by the second receiving antenna 19 and outputs it to the receiver 17.

Description

Technical Field

[0001] The present disclosure relates to a receiving device that receives a transmission radio wave of a transmitter, and a receiving method.

Background Art

[0002] Conventionally, as disclosed in Patent Document 1, a wheel nut loosening detection device that detects loosening of a wheel nut of a tire is well known. The wheel nut loosening detection device includes a sensor unit mounted on a wheel portion of a wheel, and an in-vehicle device provided on a vehicle body for receiving a radio wave transmitted from the sensor unit. The sensor unit transmits measurement data related to loosening of the wheel nut. The in-vehicle device detects the presence or absence of loosening of the wheel nut based on the measurement data received from the sensor unit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in a vehicle, for example, there are various vehicle noises (electromagnetic wave noises) output from electrical devices mounted on the vehicle. Whether the in-vehicle device can receive the transmission radio wave of the sensor unit is determined by the S / N ratio, which is the ratio of the transmission radio wave to the noise radio wave. Therefore, in order to receive the transmission radio wave of the sensor unit by the in-vehicle device without being affected by the noise source, for example, a method of reducing the noise component by separating the antenna of the in-vehicle device from the noise source can be considered. In addition to this, for example, a method of increasing the signal component by increasing the transmission output of the transmitter in order to increase the received power of the antenna can also be considered.

[0005] The antenna for an in-vehicle device is preferably placed inside the vehicle, taking into consideration factors such as wiring, waterproofing, and protection against falling. However, in the case of a truck, the cabin is not large, making it impossible to place the antenna far enough away from electrical equipment that are noise sources inside the cabin. In such cases, the antenna must be placed outside the vehicle, requiring wiring, waterproofing, and protection against falling. This results in a more complex antenna structure and increased costs. Therefore, in the case of trucks, there is a strong need to place the antenna for the in-vehicle device inside the vehicle.

[0006] Furthermore, some trucks have a metal cargo compartment on the bed. Therefore, if the on-board unit's antenna is located inside the vehicle, the radio waves transmitted from the sensor unit mounted on the rear wheel may not reach the on-board unit's antenna directly due to interference from the metal cargo compartment. In this case, it is necessary to receive diffracted waves propagating along the metal cargo compartment. However, while the noise component of the signal-to-noise ratio (S / N ratio) remains unchanged and unaffected by the cargo compartment, the signal component is affected. This can lead to a decrease in the signal component of the S / N ratio, potentially resulting in insufficient reception performance. One possible solution is to increase the transmitter's output power, but this increases power consumption, necessitating other measures. [Means for solving the problem]

[0007] A receiving device that solves the above problem is a device for receiving transmitted radio waves transmitted from a transmitter mounted on a vehicle, comprising: a first receiving antenna and a second receiving antenna arranged at positions along the propagation path of the transmitted radio waves which are diffracted by a radio wave shield provided on the vehicle, a position that receives noise waves transmitted from a noise source on the vehicle in phase, and positions spaced apart from each other; a conversion unit that converts the phase of the first received radio wave received by the first receiving antenna to the phase of the second received radio wave received by the second receiving antenna; and a combiner that combines the first received radio wave input from the conversion unit and the second received radio wave received by the second receiving antenna and outputs it to a receiver.

[0008] A receiving method for solving the aforementioned problems is a method for receiving transmitted radio waves transmitted from a transmitter mounted on a vehicle, comprising: arranging a first receiving antenna and a second receiving antenna for receiving the transmitted radio waves at positions along the propagation path of the transmitted radio waves which are diffracted by a radio wave shield provided on the vehicle, at positions where noise waves transmitted from a noise source on the vehicle are received in phase, and at positions spaced apart from each other; connecting a radio wave phase conversion unit to the first receiving antenna, and converting the phase of the first received radio wave received by the first receiving antenna to the phase of the second received radio wave received by the second receiving antenna by the conversion unit; and connecting a combiner to the second receiving antenna and the conversion unit, and combining the first received radio wave input from the conversion unit and the second received radio wave received by the second receiving antenna by the combiner and outputting it to a receiver. [Effects of the Invention]

[0009] This disclosure makes it possible to improve the receiving performance of receiving radio waves transmitted by a transmitter, even when the receiving antenna cannot be placed away from the noise source. [Brief explanation of the drawing]

[0010] [Figure 1] This is a configuration diagram of a vehicle condition detection device and a receiving device according to one embodiment. [Figure 2] This is a perspective view of a commercial vehicle. [Figure 3] This is an explanatory diagram showing the propagation path of transmitted radio waves when viewed from above a cargo truck. [Figure 4] This is a perspective view showing a general overview of the cabin's interior. [Figure 5] This waveform diagram shows the relationship between the antenna spacing and the amplitude of the composite wave. [Modes for carrying out the invention]

[0011] An embodiment of this disclosure is described below. (Vehicle condition detection device 1) As shown in Figure 1, the vehicle 2 is equipped with a vehicle state detection device 1 that detects the vehicle state by wireless communication. The vehicle state detection device 1 comprises a transmitter 3 attached to the vehicle 2 and a receiver 4 that receives transmitted radio waves Sa from the transmitter 3. The transmitter 3 transmits transmitted radio waves Sa according to the vehicle state. The vehicle state is, for example, the current state of the tires 5 of the vehicle 2. In this case, the transmitter 3 is attached to the tire 5 and transmits various information about the tire 5 along with the transmitted radio waves Sa.

[0012] Examples of vehicle condition detection devices 1 include a nut loosening detection device and a tire pressure detection device. The nut loosening detection device uses various information contained in the radio waves Sa transmitted by a transmitter 3 attached to the tire 5 to detect whether the nuts on the tire 5 are loose. The tire pressure detection device uses, for example, air pressure information contained in the radio waves Sa transmitted by a transmitter 3 attached to the tire 5 to detect the air pressure of the tire 5.

[0013] (Vehicle 2 equipped with vehicle condition detection device 1) As shown in Figure 2, the vehicle 2 is, for example, a cargo truck 9 having a metal storage compartment 8 in the cargo bed 7. Thus, it is preferable that the vehicle state detection device 1 be used in the cargo truck 9. In the cargo truck 9, the metal storage compartment 8 is located behind the cabin 10 which has seats. The metal storage compartment 8 is, for example, a sealed cargo compartment with a door that can be opened and closed. The cabin 10 is located above the front wheels and has a driver's seat and a passenger seat. The metal storage compartment 8 is located above the rear wheels 11 and is positioned to obstruct the rearward view from the cabin 10.

[0014] (Transmitter 3) As shown in Figure 2, the transmitter 3 is attached, for example, to each of the multiple tires 5 provided on the vehicle 2. The transmitter 3 transmits a radio wave Sa at a predetermined position in the rotational direction of the tire 5, or at predetermined time intervals. The radio wave Sa is, for example, a radio wave in the UHF (Ultra High Frequency) band, but radio waves of other frequencies may also be used. In the case of radio waves in the UHF band, the wavelength λ of the radio wave is, for example, about 1 m to 10 cm.

[0015] (Transmission radio wave Sa path) As shown in FIG. 3, when the receiving device 4 is arranged in the cabin 10, when receiving the transmission radio wave Sa of the transmitter 3 attached to the rear wheel 11 of the vehicle 2 by the receiving device 4, since the metal housing 8 becomes a radio wave shielding object, it is necessary to receive the radio wave that takes the path diffracted along the outer wall of the metal housing 8 (the path of the arrow Ra in FIG. 3). The transmission radio wave Sa takes such a path because the transmission radio wave Sa cannot pass through the metal object, the metal housing 8, and thus it is necessary to bypass the metal housing 8.

[0016] In the case of the truck 9, the transmission radio wave Sa transmitted from the transmitter 3 of the rear wheel 11 propagates, for example, along the outer wall of the metal housing 8 and diffracts at a substantially right angle between the metal housing 8 and the cabin 10 and propagates into this gap. Thus, the transmission radio wave Sa transmitted from the transmitter 3 of the rear wheel 11 first propagates in the vehicle longitudinal direction (the X-axis direction in FIG. 3), but takes the path of bending at a substantially right angle between the metal housing 8 and the cabin 10 and propagating in the vehicle width direction (the Y-axis direction in FIG. 3). Therefore, when the receiving device 4 is arranged in the cabin 10, it is preferable to adopt an antenna arrangement considering receiving the radio wave propagating in the vehicle width direction.

[0017] (Receiving device 4) As shown in FIG. 1, the receiving device 4 includes a pair of receiving antennas 14, a conversion unit 15, a synthesizer 16, and a receiver 17. The pair of receiving antennas 14 includes a first receiving antenna 18 and a second receiving antenna 19 arranged at positions spaced apart by a distance d from each other. The receiving device 4 (at least the pair of receiving antennas 14) is preferably arranged in the cabin 10 of the truck 9, that is, arranged inside the vehicle 2.

[0018] (Pair of receiving antennas 14) As shown in FIG. 4, a pair of receiving antennas 14 are attached to the rear window 20 of the cab 10 of the truck 9. Thus, the pair of receiving antennas 14 are arranged at positions along the transmission path of the transmitted radio wave Sa diffracted under the influence of the radio wave shielding member 12 (in this example, the metal housing 8) provided in the vehicle 2. The pair of receiving antennas 14 are arranged side by side along the vehicle width direction (the Y-axis direction in FIG. 3) at the rear window 20. As the first receiving antenna 18 and the second receiving antenna 19, various antennas such as a dipole antenna can be used.

[0019] The radio waves received by the first receiving antenna 18 and the second receiving antenna 19 are radio waves that enter by diffraction between the metal housing 8 and the cab 10. Also, the first receiving antenna 18 and the second receiving antenna 19 are arranged so as to be aligned along the traveling direction of the radio wave entering between the cab 10 and the metal housing 8 by being attached to the rear window 20 of the cab 10. Therefore, the first receiving antenna 18 and the second receiving antenna 19 receive radio waves having a phase difference corresponding to the interval d which is the interval between their arrangements.

[0020] For example, the same antenna is used for the pair of receiving antennas 14. Thereby, the pair of receiving antennas 14 are configured such that the gain of the first received radio wave Sb1 which is the radio wave obtained by receiving the transmitted radio wave Sa by the first receiving antenna 18 and the gain of the second received radio wave Sb2 which is the radio wave obtained by receiving the transmitted radio wave Sa by the second receiving antenna 19 are the same or in the vicinity. Even when there is a gain difference between the first received radio wave Sb1 and the second received radio wave Sb2, for example, an amplifier may be provided on the wiring path to reduce the gain difference. In any case, it is preferable that the pair of receiving antennas 14 do not cause a gain difference in the received radio waves.

[0021] (Conversion unit 15) As shown in Figure 1, the conversion unit 15 has a first receiving antenna 18 connected to its input and a combiner 16 connected to its output. The conversion unit 15 converts the phase of the first received radio wave Sb1 to the phase of the second received radio wave Sb2. In this example, the conversion unit 15 is a delay unit 15a that delays the first received radio wave Sb1 relative to the second received radio wave Sb2. The delay unit 15a is, for example, a delay line that generates a predetermined amount of delay in the signal flowing through the wiring. The delay unit 15a delays the wavelength λ of the transmitted radio wave Sa, which is the target of reception by the pair of receiving antennas 14, by half a wavelength. In this way, the delay unit 15a delays the phase of the first received radio wave Sb1 received by the first receiving antenna 18 by a predetermined amount and outputs the delayed first received radio wave Sb1 to the combiner 16.

[0022] (Synthesizer 16) The combiner 16 has the conversion unit 15 and the second receiving antenna 19 connected to its input, and the receiver 17 connected to its output. Any combiner can be used for the combiner 16, such as a Wilkinson combiner. The combiner 16 combines the first received radio wave Sb1 after conversion and the second received radio wave Sb2 received by the second receiving antenna 19, and outputs the combined wave Sc to the receiver 17. The receiver 17 detects the combined wave Sc input from the combiner 16. The receiver 17 reads various information contained in the transmitted radio wave Sa of the transmitter 3 from the detected combined wave Sc, and performs an operation according to the information read.

[0023] (Measures against noise wave Sn) As shown in Figure 4, the pair of receiving antennas 14 are positioned to receive the noise wave Sn transmitted from the noise source 22 of the vehicle 2 in phase. The noise source 22 is, for example, equipment installed on the instrument panel inside the vehicle (such as an audio system or a car navigation system). In this example, the pair of receiving antennas 14 are positioned at the rear window 20 of the cabin 10, thereby receiving the noise wave Sn generated from the noise source 22 in phase. Note that "in phase" here does not only mean perfectly in phase, but also includes "almost in phase" where the phase is significantly smaller. When the pair of receiving antennas 14 receive the noise wave Sn in phase, one of these radio waves is delayed by the delay unit 15a, so the noise wave Sn cancels out when combined.

[0024] (Effect of the embodiment) Next, the operation of the receiving device 4 in this embodiment will be described. As shown in Figure 3, when a transmitted radio wave Sa is transmitted from a transmitter 3 attached to the rear wheel 11 of vehicle 2, assume that the transmitted radio wave Sa diffracts and enters the space between the metal housing 8 and the cabin 10 from the left side of the vehicle body. In this case, for example, if the distance d between the first receiving antenna 18 and the second receiving antenna 19 is 1 / 2 (=180 degrees) of the wavelength λ of the transmitted radio wave Sa, then if the phase of the second received radio wave Sb2 received by the second receiving antenna 19 is "0 degrees", the phase of the delayed first received radio wave Sb1 becomes "360 degrees", and the two radio waves become in phase. Therefore, when the delayed first received radio wave Sb1 and the second received radio wave Sb2 are combined, the wave height of the combined wave Sc becomes twice as high. Thus, it becomes possible to obtain the signal component of the radio wave received by the receiving device 4 with sufficient strength.

[0025] Similarly, suppose the transmitted radio wave Sa from transmitter 3 diffracts and enters the space between cabin 10 and metal storage compartment 8 from the right side of the vehicle. In this case, for example, if the distance d between the first receiving antenna 18 and the second receiving antenna 19 is 1 / 2 (=180 degrees) of the wavelength λ of the transmitted radio wave Sa, then if the phase of the second received radio wave Sb2 received by the second receiving antenna 19 is "180 degrees", then the phase of the delayed first received radio wave Sb1 will also be "180 degrees", and similarly the two radio waves will be in phase. Therefore, in this case as well, the wave height of the composite wave Sc, which is a combination of the delayed first received radio wave Sb1 and the second received radio wave Sb2, will be doubled, making it possible to obtain the signal component of the radio wave received by the receiving device 4 with sufficient strength.

[0026] Furthermore, the first receiving antenna 18 and the second receiving antenna 19 also receive the noise wave Sn transmitted from the noise source 22 inside the vehicle. In this example, the first receiving antenna 18 and the second receiving antenna 19 are mounted on the rear window 20 of the cabin 10 so as to receive the noise wave Sn in phase. As a result, the delayed noise component received by the first receiving antenna 18 and the noise component received by the second receiving antenna 19 are out of phase and cancel each other out. Therefore, it is possible to eliminate the noise component from the radio waves received by the receiving device 4. Note that since the first receiving antenna 18 and the second receiving antenna 19 receive the noise wave Sn in phase, the noise components that are canceled out are not affected by the interval d.

[0027] In this example, a pair of receiving antennas 14 are positioned at the rear window 20 of the cabin 10 to receive the transmitted radio waves Sa that diffract and enter the space between the metal housing 8 and the cabin 10. However, this brings the pair of receiving antennas 14 close to the noise source 22, causing them to receive the noise wave Sn. Therefore, in this example, the pair of receiving antennas 14 are positioned so that the noise wave Sn is received in phase, and the noise wave Sn received by one of the pair of receiving antennas 14 is delayed by the delay unit 15a, thereby canceling out the noise component. As a result, the noise component of the S / N ratio is reduced, making it possible to increase the S / N ratio. Thus, sufficient receiving performance of the receiving device 4 is ensured.

[0028] Figure 5 is a waveform diagram showing the relationship between the distance d between the first receiving antenna 18 and the second receiving antenna 19 and the amplitude of the composite wave Sc. The amplitude of the composite wave Sc peaks when the distance d is λ / 2 (180 degrees in terms of the phase difference of the signals) and decreases as the distance d narrows. Therefore, it can be seen that in order to obtain the highest signal component when receiving radio waves with the receiving device 4, the distance d between the antennas should be λ / 2 or a value close to it.

[0029] Generally, antennas placed in close proximity influence each other. For this reason, in the first receiving antenna 18 and the second receiving antenna 19 in this example, if the antenna type is a dipole antenna, the spacing d may be set to a small value, specifically about 0.2λ, in order to make them function similarly to the director of a Yagi antenna. Even in such a case, since the noise component is canceled out by receiving the noise wave Sn in phase, a certain level of received strength is ensured, even if the signal component becomes small.

[0030] Therefore, in this example, since the noise component of the signal-to-noise ratio is minimized, communication is established if a radio wave with power that satisfies the desired signal-to-noise ratio relative to the ideal noise floor, i.e., the minimum signal-to-noise ratio required to detect the radio wave, can be received. As a result, it is considered that sufficient communication performance can be satisfied even if the interval d is in the range of, for example, 0.2λ to 0.7λ. For the above reasons, it can be said that an interval d of 0.2λ or greater is preferable.

[0031] Furthermore, when an experiment was conducted to see if it was possible to receive UHF band radio waves used in the tire pressure detection device by actually placing an antenna inside the cabin 10, it was found that when transmitting radio waves at a transmission power that met the regulations, the radio waves themselves could be received by the antenna inside the cabin 10, but the noise component received from the noise source 22 was large, and the desired S / N ratio could not be satisfied. However, if the noise component can be sufficiently reduced using the receiving device 4 in this example, it becomes possible to increase the S / N ratio, so it becomes possible to receive radio waves even at the transmission power that meets the regulations. Therefore, in this respect as well, this example can be said to be superior.

[0032] (Effects of the embodiment) The following effects can be obtained with the receiving device 4 (receiving method) configuration of this embodiment.

[0033] (1) The receiving device 4, which receives the transmitted radio waves Sa transmitted from the transmitter 3 mounted on the vehicle 2, comprises a pair of receiving antennas 14 (a first receiving antenna 18 and a second receiving antenna 19), a conversion unit 15, and a combiner 16. The first receiving antenna 18 and the second receiving antenna 19 are positioned along the propagation path of the transmitted radio waves Sa which are diffracted by the radio wave shield 12 provided on the vehicle 2, at a position where they receive the noise waves Sn transmitted from the noise source 22 of the vehicle 2 in phase, and at a distance d from each other. The conversion unit 15 converts the phase of the first received radio wave Sb1 received by the first receiving antenna 18 to the phase of the second received radio wave Sb2 received by the second receiving antenna 19. The combiner 16 combines the first received radio wave Sb1 input from the conversion unit 15 and the second received radio wave Sb2 received by the second receiving antenna 19 and outputs it to the receiver 17.

[0034] In this configuration, a phase difference occurs between the first received radio wave Sb1 and the second received radio wave Sb2, corresponding to the distance d between the first receiving antenna 18 and the second receiving antenna 19. However, by converting the first received radio wave Sb1 using the conversion unit 15, it is possible to suppress the phase difference between the first received radio wave Sb1 and the second received radio wave Sb2. Therefore, when the first received radio wave Sb1 and the second received radio wave Sb2 are combined, a composite wave Sc with amplified signal is obtained. As a result, it becomes possible to receive the transmitted radio wave Sa from the transmitter 3 with an amplified wave, and thus the signal-to-noise ratio (S / N ratio), which is the ratio of the signal component of the transmitted radio wave Sa to the noise component of the noise wave Sn, can be increased.

[0035] Furthermore, the first receiving antenna 18 and the second receiving antenna 19 are positioned to receive the noise wave Sn transmitted from the noise source 22 of the vehicle 2 in phase. Therefore, the noise wave Sn received by the first receiving antenna 18, after conversion by the conversion unit 15, has a waveform that is nearly inverse phase with the noise wave Sn received by the second receiving antenna 19. As a result, when the converted first received radio wave Sb1 and the second received radio wave Sb2 are combined, the noise waves Sn cancel each other out. This further contributes to improving the signal-to-noise ratio. Thus, even if the pair of receiving antennas 14 cannot be placed away from the noise source 22, the receiving performance of the receiving device 4 when receiving the transmitted radio wave Sa from the transmitter 3 can be improved.

[0036] (2) The conversion unit 15 is a delay unit 15a that generates a phase difference by delaying the first received radio wave Sb1 relative to the second received radio wave Sb2. With this configuration, by using a simple configuration with a delay circuit, the first received radio wave Sb1 can be delayed by a predetermined amount, and the noise wave Sn of the first received radio wave Sb1 and the noise wave Sn of the second received radio wave Sb2 can be made out of phase.

[0037] (3) Vehicle 2 is a cargo truck 9 having a metal storage compartment 8 as a radio wave shield 12 on its cargo bed 7. The transmitter 3 is mounted on a tire 5 (in this example, the rear wheel 11) located below the metal storage compartment 8. With this configuration, when a radio wave Sa is transmitted from the transmitter 3 mounted on the rear wheel 11 of the cargo truck 9, the radio wave Sa propagates along the metal storage compartment 8 of the cargo truck 9. However, even if the radio wave Sa of the transmitter 3 mounted on the rear wheel 11 of the cargo truck 9 takes such a propagation path, the receiving device 4 in this example ensures that the signal-to-noise ratio of the size necessary for reception is secured. Therefore, the radio wave Sa of the transmitter 3 mounted on the rear wheel 11 of the cargo truck 9 can be received by the receiving device 4.

[0038] (4) The first receiving antenna 18 and the second receiving antenna 19 are located inside the cabin 10 of the cargo truck 9. Specifically, the first receiving antenna 18 and the second receiving antenna 19 are mounted on the rear window 20 of the cabin 10. The transmitted radio waves Sa, which are transmitted from the transmitter 3 mounted on the rear wheel 11 and propagate along the metal housing 8, have a large component that passes between the metal housing 8 and the cabin 10. Therefore, if the pair of receiving antennas 14 are located on the rear window 20 of the cabin 10, it will be possible to efficiently receive the transmitted radio waves Sa that propagate between the metal housing 8 and the cabin 10. Thus, this will further contribute to improving the receiving performance of the receiving device 4.

[0039] (5) The first receiving antenna 18 and the second receiving antenna 19 are configured such that the gain of the first received radio wave Sb1 and the gain of the second received radio wave Sb2 are the same or approximately the same. With this configuration, it is possible to keep the difference in amplitude between the first received radio wave Sb1 and the second received radio wave Sb2 small, so that a composite wave Sc suitable for signal amplification and noise cancellation can be generated, for example. This further contributes to improving the receiving performance of the receiving device 4.

[0040] (6) The delay unit 15a delays the first received radio wave Sb1, which is the transmitted radio wave Sa received by the first receiving antenna 18, by half a wavelength. The distance d between the first receiving antenna 18 and the second receiving antenna 19 is set to half the wavelength λ of the transmitted radio wave Sa or a value close to it. With this configuration, it is possible to maximize the amplitude of the composite wave Sc of the first received radio wave Sb1 and the second received radio wave Sb2. Therefore, it contributes further to improving the receiving performance of the receiving device 4.

[0041] (Other embodiments) This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0042] The conversion unit 15 may use a method that employs phase delay, a method that employs group delay using a filter, or an amplifier that inverts the phase. The delay value of the delay unit 15a is not limited to λ / 2; it may be changed to any other value. In other words, the delay value of the delay unit 15a should be set to an optimal value corresponding to the distance d between the first receiving antenna 18 and the second receiving antenna 19.

[0043] Even if there is no gain difference between the first receiving antenna 18 and the second receiving antenna 19, the received signal may be amplified by using an amplifier. The placement of the transmitter 3 is not limited to the tire 5 (rear wheel 11); any location where radio waves are difficult to reach the receiver 4 is acceptable.

[0044] The placement of the pair of receiving antennas 14 is not limited to the rear window 20 of the vehicle 2 (cabin 10), but may be in other locations within the cabin 10, such as the door window, ceiling, rear wall, side wall, or windshield.

[0045] The pair of receiving antennas 14 may be mounted, for example, in a dedicated window for antenna placement provided in the cabin 10, or in a location in the cabin 10 where radio waves can penetrate easily.

[0046] The radio wave shielding material 12 is not limited to the metal housing chamber 8; any metal component is acceptable. • Cargo vehicles 9 include flatbed trucks, van-type vehicles, refrigerated trucks, chilled trucks, trailers, tank trucks, heavy equipment transport vehicles, dump trucks, etc.

[0047] The transmitter 3 may be attached to tires 5 other than the rear wheels 11. The transmitter 3 is not limited to being attached to the tire 5, but may be any other component mounted on the vehicle.

[0048] The vehicle condition detection device 1 is not limited to a nut loosening detection device or a tire pressure detection device; it may be changed to other devices. Vehicle 2 is not limited to the cargo truck 9; it may be a vehicle of other purposes.

[0049] The receiver 17 may be composed of [1] one or more processors operating according to a computer program (software), or [2] a combination of such processors and one or more dedicated hardware circuits, such as application-specific integrated circuits (ASICs), that perform at least some of the various processes. The processor includes a CPU and memory such as RAM and ROM, and the memory stores program code or instructions configured to cause the CPU to perform the processes. The memory (computer-readable medium) includes any available medium that can be accessed by a general-purpose or dedicated computer. Alternatively, instead of a computer including the above-mentioned processor, a processing circuit composed of one or more dedicated hardware circuits that perform all of the various processes may be used.

[0050] This disclosure is described in accordance with the embodiments, but is not limited to the structures of these embodiments and includes various modifications and variations within the equivalence range. This disclosure also includes various combinations and forms, as well as combinations and forms of one, more, or fewer of these elements. [Explanation of symbols]

[0051] 2...vehicle, 3...transmitter, 4...receiver, 5...tire, 7...cargo bed, 8...metal storage compartment, 9...cargo truck, 10...cabin, 11...rear wheels, 12...radio wave shield, 15...converter, 15a...delay unit, 16...combiner, 17...receiver, 18...first receiving antenna, 19...second receiving antenna, 20...rear window, 22...noise source, Sa...transmitted radio wave, Sb1...first received radio wave, Sb2...second received radio wave, Sn...noise wave, d...interval.

Claims

1. A receiving device that receives transmitted radio waves from a transmitter mounted on a vehicle, A first receiving antenna and a second receiving antenna are positioned at locations along the propagation path of the transmitted radio waves, which are diffracted by a radio wave shield installed on the vehicle, at locations that receive noise waves transmitted from a noise source on the vehicle in phase, and at locations that are spaced apart from each other. A conversion unit that converts the phase of the first received radio wave received by the first receiving antenna to the phase of the second received radio wave received by the second receiving antenna, A receiving device comprising a combiner that combines the first received radio wave input from the conversion unit and the second received radio wave received by the second receiving antenna and outputs it to a receiver.

2. The receiving device according to claim 1, wherein the conversion unit is a delay unit that generates a phase difference by delaying the first received radio wave relative to the second received radio wave.

3. The aforementioned vehicle is a cargo truck having a metal storage compartment in its cargo bed that serves as the aforementioned radio wave shielding device. The receiving device according to claim 1, wherein the transmitter is attached to a tire located below the metal housing chamber.

4. The receiving device according to claim 3, wherein the first receiving antenna and the second receiving antenna are located inside the cabin of the cargo vehicle.

5. The receiving device according to claim 1, wherein the first receiving antenna and the second receiving antenna are configured such that the gain of the first received radio wave and the gain of the second received radio wave are the same or approximately the same.

6. The delay unit delays the first received radio wave, which is the transmitted radio wave received by the first receiving antenna, by half a wavelength. The receiving device according to claim 2, wherein the distance between the first receiving antenna and the second receiving antenna is set to half or a value close to the wavelength of the transmitted radio wave.

7. A receiving method for receiving transmitted radio waves from a transmitter mounted on a vehicle, The first and second receiving antennas for receiving the transmitted radio waves are positioned along the propagation path of the transmitted radio waves, which are diffracted by the radio wave shielding provided on the vehicle, at a position where they receive noise waves transmitted from the noise source of the vehicle in phase, and at positions spaced apart from each other. A phase conversion unit is connected to the first receiving antenna, and the phase of the first received radio wave received by the first receiving antenna is converted by the conversion unit to the phase of the second received radio wave received by the second receiving antenna. A receiving method comprising connecting a combiner to the second receiving antenna and the conversion unit, and combining the first received radio wave input from the conversion unit and the second received radio wave received by the second receiving antenna using the combiner and outputting it to a receiver.

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