JP2013026970A - Radio receiver and radio reception method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent interferences due to intermodulation in multicarrier system radio reception.SOLUTION: In a radio receiver, a first radio signal transmitted by a multicarrier modulation system is received and then demodulated. The radio receiver includes: reception means of receiving the first radio signal and second radio signals which are transmitted in frequency bands near a frequency band in which the first radio signal is transmitted; sensing means of detecting carrier waves equal to or greater than a prescribed value in signal intensity from among the second radio signals received by the reception means; interference wave detection means of calculating the frequency band of an intermodulation wave generated by the detected carrier wave; and demodulation means of demodulating the first radio signal, at which time, if the frequency band of the intermodulation wave is included in the frequency band in which the first radio signal is transmitted, a carrier wave which includes the frequency band of the intermodulation wave is excluded from among carrier waves included in the first radio signal.

Description

  The present invention relates to a radio receiver and a radio reception method.

  In recent years, road-to-vehicle / vehicle-to-vehicle communication systems for reducing traffic accidents by providing information to vehicles and drivers and exchanging information between roads and vehicles and vehicles have been proposed.

Currently, the use of the 700 MHz band as a frequency to be used for realizing a road-to-vehicle / vehicle-to-vehicle communication system is being studied. This 700 MHz band frequency is also planned to be used in mobile phones using the LTE (Long Term Evolution) system in addition to road-to-vehicle and inter-vehicle communication systems.

  Referring to the 700 MHz band radio wave reorganization plan, there is a plan to arrange a frequency for road-to-vehicle / vehicle-to-vehicle communication systems between the uplink frequency and the downlink frequency of LTE mobile phones (non-patent document 1) 700-3).

  On the other hand, when there are a plurality of wireless communication systems in adjacent frequency bands, radio wave interference may be a problem. The wireless communication device described in Patent Document 1 is an invention related to cognitive radio, and when there are a plurality of wireless systems in the vicinity, metric information indicating the degree of association between the own system and another system is used to transmit radio waves between the systems. The degree of interference is judged. When there is a possibility of interference, the transmission of the own system is stopped and the output is reduced to avoid radio wave interference.

  The wireless communication device described in Patent Document 2 stores an area in the wireless device where radio interference between the own system and a wireless communication system using another frequency band is likely to occur. The ease of radio wave interference is determined based on the information and the location information of the aircraft. In an area where interference is likely to occur, switching to a communication method that reduces the degree of radio wave interference achieves avoidance of radio wave interference.

JP 2009-253450 A JP 2011-015115 A

“Mobile Phone Frequency Effective Use Policy Committee (51st) Handout (Reference 1)”, [online] Information and Communication Council Information and Communication Technology Subcommittee, [Search June 20, 2011], Internet < URL: http://www.soumu.go.jp/main_sosiki/joho_tsusin/policyreports/joho_tsusin/keitai_syuuha/39264_1.html>

  In the invention described in Patent Document 1, the possibility of interference is determined by a signal that informs the surroundings of the distance to other wireless systems and the presence of the own wireless system, and interference is avoided by stopping transmission or suppressing output. ing. Further, in the invention described in Patent Document 2, it is determined whether the device itself is located in an area where interference is likely to occur, and interference is avoided by changing the communication method.

  Even when using a road-to-vehicle / vehicle-to-vehicle communication system (hereinafter referred to as an ITS system), radio wave interference with an LTE mobile phone system (hereinafter referred to as an LTE system) having a close band may occur. However, since the service areas of the ITS system and the LTE system overlap and it is possible to use a mobile phone in the vicinity of the ITS equipment installed in the car, information such as the distance between systems and the area of the wireless service is not available. Therefore, the invention according to Patent Document 1 or 2 cannot solve this problem.

  In particular, since a cellular phone terminal generally does not have high filtering performance of a transmission circuit, an intermodulation wave that interferes with other systems may be generated in a band other than the transmission frequency band of the own system.

  When an LTE mobile phone is used in the vicinity of an ITS device, the frequency used by the receiver (vehicle terminal) and the frequency used by the transmitter (mobile phone terminal) are close to each other, Since the physical distance between the receiver and the transmitter is also close, there is a problem that the receiver is susceptible to interference by intermodulation waves.

  Note that such a problem of radio wave interference can occur not only between the ITS system and the LTE system, but also in a wireless communication system according to another standard.

  In order to solve such problems, even when communication is performed using adjacent frequencies in the vicinity of a receiver using multicarrier radio, radio communication that can receive without being affected by interference A device is sought.

  The present invention has been made in consideration of the above-described problems, and an object of the present invention is to be able to receive a signal without degrading quality even when receiving interference due to intermodulation in multicarrier radio reception.

  In order to achieve the above object, the radio receiver according to the present invention can receive a signal without degrading quality even when it receives interference due to intermodulation by the following means.

  A radio receiver according to the present invention is a radio receiver for receiving and demodulating a first radio signal transmitted by a multicarrier modulation method, wherein the first radio signal and the first radio signal are transmitted. A second wireless signal transmitted in a frequency band in the vicinity of the frequency band to be received, and a signal strength of a second wireless signal received by the receiving means is greater than or equal to a predetermined value Sensing means for detecting a carrier wave, interference wave detecting means for calculating a frequency band of an intermodulation wave generated by the detected carrier wave, and a frequency band of the intermodulation wave being a frequency at which the first radio signal is transmitted Demodulating means for demodulating the first radio signal by excluding a carrier including the frequency band of the intermodulation wave among the carriers included in the first radio signal when included in the band; Characterized in that it.

  The radio receiver according to the present invention has means for sensing adjacent frequency bands, and calculates a frequency at which an intermodulation wave appears when a signal is detected, and the intermodulation wave is included in the frequency band used by itself. If so, demodulation is performed by excluding carrier waves (subcarriers) that are interfered by intermodulation waves. With this configuration, it is possible to receive a signal without degrading quality even when the frequency band with another system is close.

Further, the demodulating means excludes the carrier wave including the frequency band of the intermodulation wave when the signal strength of the carrier wave contained in the second radio signal satisfies a predetermined condition, and outputs the first radio signal. You may make it demodulate.

  The predetermined condition is a condition for determining whether the intensity of the signal causing the interference is strong enough to affect the demodulation of the interfered wave or weak enough not to affect the interference wave. For example, it can be defined as a case where the power difference from the target signal is a certain value or less. With this configuration, it is possible to determine whether or not the intermodulation wave has an effect on demodulation. The problem of exclusion can be avoided.

  The demodulating means further includes means for detecting an error generated during demodulation, and when it is determined that demodulation is not performed normally, the demodulation means excludes the carrier wave including the frequency band of the intermodulation wave, and The first radio signal may be demodulated.

  With this configuration, it is possible to exclude subcarriers including intermodulation waves only when the data cannot be demodulated normally, thereby reducing processing overhead.

  Preferably, the modulation method of the first radio signal is OFDM, and the modulation method of the second radio signal is SC-FDMA.

  The radio signal based on SC-FDMA assumes a mobile phone based on the LTE system. When multiple intermodulation waves appear in the frequency band used by the local system, if the subcarriers that are subject to interference are sequentially removed from the demodulation target, the amount of information will be insufficient and demodulated at a certain level. There may be cases where it becomes impossible. However, assuming that an LTE mobile phone is used in the vicinity of the wireless receiver, the band used by each mobile phone is not wide, so even if the signal strength of each intermodulation wave is strong, A large number of intermodulation waves do not appear so that they cannot be demodulated. That is, it can be expected that the problem of radio wave interference is solved by excluding subcarriers including intermodulation waves.

In addition, the interference wave detection means, where a is a carrier frequency detected by the sensing means, and b is a center frequency of a frequency band used for transmission of the second radio signal, that is, a DC subcarrier center frequency. The frequencies A and B represented by the expressions (1) and (2) may be calculated as the frequencies of the intermodulation waves.
A = 4b-3a Formula (1)
B = 3a-2b Formula (2)

  Since the appearance position of the intermodulation wave can be calculated by a certain algorithm, the frequencies of all intermodulation waves appearing in the frequency band of the interfered system can be specified by the equations (1) and (2). it can.

  According to the present invention, it is possible to receive a signal without degrading quality even when receiving interference due to intermodulation in multicarrier radio reception.

It is a figure showing the frequency band of a LTE system and an ITS system. It is a figure showing a mode that a LTE system interferes with an ITS system. It is a figure showing the function structure of the radio receiver in this invention. It is a process flowchart of the radio | wireless receiver in this embodiment. It is a figure showing the radio wave allocation in the frequency band of each system of LTE and ITS. It is a figure showing the frequency calculation method of a 7th-order intermodulation wave. It is a figure showing the frequency calculation method of a 5th-order intermodulation wave. It is a figure which shows the specific example of the electromagnetic wave interference between LTE and ITS systems. It is a figure which shows the signal strength difference of the subcarrier used as interference, and a to-be-interfered wave. It is a process flowchart of the radio | wireless receiver in the modification of this embodiment.

(Technical solution)
The technical problem will be described by taking radio wave interference between the LTE system and the ITS system as an example. FIG. 1 is an example in which the frequency of the ITS system is arranged between the uplink frequency and the downlink frequency of the LTE system. Each frequency has a band of several MHz, and a vacant frequency called a guard band is arranged between systems in order to prevent mutual interference.

  The cause of the radio wave interference between the LTE system and the ITS system will be described with reference to FIG. In multicarrier radio using a plurality of mutually orthogonal subcarriers, when a signal is transmitted using a specific subcarrier, an intermodulation wave with its own DC subcarrier may be generated depending on the circuit configuration of the radio transmitter. is there. The intermodulation wave is a signal having the same frequency width as that of the subcarrier and appearing symmetrically with a specific frequency as an axis, and third-order, fifth-order, and seventh-order intermodulation waves are generated by the generation mechanism. An intermodulation wave that appears around the center of the transmission frequency band is called a third-order intermodulation wave. Also, the third order intermodulation wave with the subcarrier as an axis and the intermodulation wave that appears in the object is called the fifth order intermodulation wave, and the intermodulation wave that appears symmetrically with the subcarrier with the third order intermodulation wave as the axis, This is called a seventh-order intermodulation wave.

  A guard band for preventing interference is arranged between the systems. For example, when the distance between the center frequency of the LTE system and the subcarrier is 5 MHz, the third-order intermodulation wave is 10 MHz higher than the signal. The seventh-order intermodulation wave appears at a position 20 MHz higher than the signal. For this reason, there is a possibility that the intermodulation wave appears in the allocated frequency of the ITS system beyond the guard band and interferes with the signal used by the ITS system. This problem can occur even outside of between the LTE system and the ITS system.

  In order to solve this problem, it is necessary to adopt a reception system that can eliminate the influence of interference caused by intermodulation waves on the receiver side.

  On the other hand, in multi-carrier wireless communication, each subcarrier has a redundant component, so even if some subcarriers cannot be received, the information from the redundancy of other subcarriers can be obtained. Sometimes it can be restored. Since the ITS system also employs a multi-carrier scheme, even if the level of a specific subcarrier is weak and reception is not possible, the redundant portion of the received data obtained from the remaining subcarriers is used for encoding, etc. There is a possibility that received data can be obtained correctly by calculation (error correction). However, when the signal intensity of the intermodulation wave is strong, the signal of the interfered wave also appears strong, so that the receiver attempts to demodulate it, and as a result, correct data cannot be obtained. This is particularly noticeable when the LTE terminal that causes interference is in the vicinity of the ITS terminal. Specifically, when an LTE mobile phone is used in an automobile equipped with an ITS terminal, an uplink frequency band may interfere with the ITS system, and the ITS terminal may not be able to correctly demodulate received data. That is, even if an error correction technique is used, the above-described problem cannot be solved.

In order to solve this problem, the radio receiver according to the present invention determines whether or not an intermodulation wave caused by an adjacent system exists in the frequency band used by the own system. The subcarriers to be demodulated are excluded from the target of demodulation, and the signal is demodulated using only normal subcarriers. Specific embodiments will be described below.

(Configuration of wireless receiver)
An outline of the wireless receiver in this embodiment will be described. FIG. 3 is a diagram showing the configuration of the wireless receiver in this embodiment.

  The receiving unit 34 is means for receiving both the frequency band used in the ITS system and the frequency band used in the LTE system through the antenna 31. The receiving unit 34 is a front-end unit for receiving a radio signal based on a multicarrier system, which includes an amplifier that amplifies a signal, a down converter that converts the amplified signal into a baseband signal, and the like. Of the received signals, signals in the frequency band corresponding to the ITS system are transmitted to the demodulator 35, and signals in the frequency band corresponding to the LTE system are transmitted to the sensing unit 32.

The sensing unit 32 is means for acquiring a signal in a frequency band used in the LTE system and determining a resource block being used. In the SC-FDMA (Single Carrier Frequency Division Multiple Access) system used by the uplink of the LTE system, radio wave resources are allocated in units of resource blocks including a plurality of subcarriers. By detecting a subcarrier in which communication is performed, a resource block in use can be specified. Details of the operation of the sensing unit 32 will be described later.

  The interference wave detection unit 33 is a means for estimating whether or not an intermodulation wave that interferes with the ITS system is generated based on the frequency of the resource block in use determined by the sensing unit 32. Specifically, the frequency at which the intermodulation wave is expected to be calculated is calculated using the frequency detected by the sensing unit 32 and the upper limit value and the lower limit value of the frequency determined for the LTE system. The calculation formula and calculation method will be described later.

  The demodulator 35 is means for demodulating the baseband signal output from the receiver 34 into a bit string. The demodulating unit 35 is a multi-purpose A / D converter that converts a baseband signal into a digital signal, a GI removing unit that removes a guard interval (GI), and a fast Fourier transform (FFT) unit that obtains each subcarrier. Means for demodulating a carrier-based radio signal are included. Further, the demodulation unit 35 acquires the frequency of the intermodulation wave calculated by the interference wave detection unit 33, and excludes interfering subcarriers when the appearance of the intermodulation wave is expected within the frequency band to be demodulated by itself. And has a function of demodulating. A detailed method will be described later.

  The information processing unit 36 is means for performing information processing using the digital data demodulated by the demodulation unit 35. When data is output from the wireless receiver to an external terminal, the information processing unit 36 may convert the data into a desired format.

  Details of each means will be described below with reference to FIG. 4 which is an operation flowchart of the wireless receiver according to the present invention.

(Sensing method)
When the wireless receiver according to the present invention starts operating, the sensing unit 32 performs sensing of adjacent frequency bands (S10). FIG. 5 is a diagram showing radio wave allocation in the frequency band used by the sensing target LTE system. The LTE system under consideration of frequency allocation has a band of 5 MHz to 20 MHz, and is configured by resource blocks each having a width of 180 kHz. Twelve subcarriers (15 kHz × 12 = 180 kHz) having a width of 15 kHz are allocated to one resource block, and radio wave resources are allocated to LTE terminals in units of resource blocks.

  The sensing unit 32 detects a subcarrier in which communication is performed in the frequency band assigned to the LTE system (S11). In subcarrier detection, it may be determined that communication is being performed when the level of the received signal is equal to or higher than a predetermined value. When a subcarrier in which communication is performed is detected, it is determined that there is an LTE communication terminal in the vicinity, and a resource block including the frequency band of the subcarrier is specified (S12). When a subcarrier in which communication is performed is not detected, it is determined that there is no LTE communication terminal in the vicinity, and no resource block is specified.

  A specific example will be described with reference to FIG. For example, when 745 to 750 MHz is allocated to the LTE system and resource blocks are arranged in order from the lower limit of the frequency, when the first and second blocks are used, 745.0 MHz to 745 It can be seen that up to 36 MHz is in use. The frequency of the identified resource block is sent to the interference wave detection unit 33.

(Specification of seventh-order intermodulation wave)
Next, the interference wave detection unit 33 calculates the frequency of the intermodulation wave expected to appear in the frequency band assigned to the ITS system (S13).

  FIG. 6 shows a pattern in which a seventh-order intermodulation wave is generated. Here, it is assumed that the frequency of the resource block in which communication is performed is f1, and the center frequency of the frequency band used in the LTE system is f0. Note that the resource block has a frequency width of 180 kHz, but here, the center frequency of the resource block will be described as f1 for convenience. Of course, the frequency band to be interfered with may be calculated using a frequency other than the center.

  In general, SC-FDMA adopted in LTE uplink, such as SC-FDMA, which transmits signals using subcarriers, has a frequency different from the target subcarrier due to intermodulation in the radio circuit. In some cases, a signal having the same frequency bandwidth as the subcarrier may appear. The intermodulation wave appears at a position symmetrical to the signal with the center frequency f0 of the transmission frequency band as an axis. This is called a third-order intermodulation wave, and its frequency can be expressed by an expression of f0− (f1−f0) = 2f0−f1.

  In addition, an intermodulation wave may appear in the upper frequency band with the third-order intermodulation wave as an axis. This is called a seventh-order intermodulation wave, and the frequency thereof can be expressed by the following formula: f2 + (f2-f1) = 2f2-f1 = 2 (2f0-f1) -f1 = 4f0-3f1. Since the seventh-order intermodulation wave appears outside the frequency band assigned to the LTE system, the interference wave detection unit 33 uses a band of 180 kHz (up and down 90 kHz) centered on (4f0-3f1) in its own system. If it overlaps with the frequency band, it can be determined that the ITS system is subject to interference by LTE.

  The frequency band used by the ITS system is 10 MHz, and is divided into 53 subcarriers as shown in FIG. When the above-described intermodulation wave overlaps with the subcarrier, since the corresponding subcarrier can be predicted to be disturbed by interference, the interference wave detection unit 33 transmits information on the corresponding frequency to the demodulation unit 35.

For example, when the LTE system frequency allocation is 740 to 750 MHz, the ITS system frequency allocation is 755 MHz or more, and 740 MHz to 740.18 MHz is used in communication by LTE, f0 = 745.0 MHz, f1 = 740.09 MHz Therefore, it can be seen that the seventh-order intermodulation wave appears in a range of ± 90 kHz (759.64 MHz to 759.82 MHz) centered on 4 × 745.0−3 × 740.09 = 759.73 MHz.

(Specification of fifth-order intermodulation wave)
As in the case of explaining the seventh-order intermodulation wave in FIG. 6, FIG. 7 shows a pattern in which the fifth-order intermodulation wave is generated. Similarly to the seventh-order intermodulation wave, the center frequency of the resource block in which communication is performed is f1, and the center frequency of the transmission frequency band used by the LTE system is f0.

  When the resource block in which communication is performed is above the center frequency, the third-order intermodulation wave appears symmetrically on the lower frequency side with the center frequency f0 of the assigned band as an axis. The frequency can be similarly expressed by the expression 2f0-f1.

  In this case, the intermodulation wave f3 may appear at a position symmetrical to the third-order intermodulation wave with the resource block in which communication is performed as an axis. This is called a fifth-order intermodulation wave, and the frequency thereof can be expressed by an expression of f1 + (f1−f2) = 2f1−f2 = 2f1− (2f0−f1) = 3f1−2f0. Similarly, since the fifth-order intermodulation wave also appears outside the frequency band assigned to the LTE system, the interference wave detector 33 has a band of 180 kHz (up and down 90 kHz) centered on (3f1-2f0) in its own system. When it overlaps with the frequency band to be used, it can be determined that the ITS system receives interference by LTE.

  When the above-described intermodulation wave overlaps with the subcarrier, since the corresponding subcarrier can be predicted to be disturbed by interference, the interference wave detection unit 33 transmits the information of the corresponding frequency to the demodulation unit 35.

For example, the LTE system frequency allocation is 740 to 750 MHz, the ITS system frequency allocation is 755 MHz or higher, and 749.82 MHz to 750 MHz is LT.
When used in communication by E, f0 = 745.0 MHz and f1 = 749.91 MHz, so the fifth-order intermodulation wave is centered on 3 × 749.91-2 × 745.0 = 759.73 MHz. It can be seen that it appears in a range of ± 90 kHz (759.64 MHz to 759.82 MHz).

  6 and 7 show examples in which the fifth-order and seventh-order intermodulation waves appear in the frequency band higher than the allocation frequency of the LTE system, but appear in the lower frequency band depending on the position of the resource block for communication. In some cases. Therefore, even when the LTE system is operated in a higher frequency band than the ITS system, radio wave interference can occur. Even in this case, the frequency of the intermodulation wave can be obtained by the above-described equation.

(Judgment of whether demodulation is possible)
Next, the process of the demodulator 35 will be described. If no LTE terminal in communication is detected in step S11, the demodulator 35 demodulates the signal using all subcarriers received from the receiver 34 (S15), and uses the acquired data as an information processor. 36.

  On the other hand, when the intermodulation wave is detected in step S13, the demodulator 35 demodulates the signal by excluding the subcarrier located at the position overlapping the intermodulation wave (S14). The overlap with the intermodulation wave is performed by comparing the calculated frequency band of the intermodulation wave with the frequency band of the subcarrier used by the own system. For example, when it is calculated that the intermodulation wave appears at a position of 753 MHz ± 90 kHz and the lower limit of the band of a certain subcarrier is 753 MHz, the two overlap each other, so that the subcarrier is excluded from demodulation.

  Each subcarrier is demodulated by performing an FFT (Fast Fourier Transform) operation using transmission parameters such as a transmission mode and a guard interval ratio. When excluding a specific subcarrier from demodulation, FFT processing is not performed on the subcarrier, and target data is acquired by combining only the demodulation results of other subcarriers.

  FIG. 8 shows an example where the subcarrier used by the ITS system and the calculated frequency band of the intermodulation wave overlap. Of the 53 subcarriers used by the ITS system, two subcarriers No. 5 and No. 6 are affected by interference in this example. Therefore, the demodulation unit 35 performs demodulation by excluding the corresponding two subcarriers, and transmits the acquired data to the information processing unit 36.

  Note that the overlap between the intermodulation wave and the subcarrier may be excluded if the frequency overlaps at least partly, or may be excluded if the frequency band exceeds a certain frequency.

  Note that the flowchart of FIG. 4 may be executed continuously at regular intervals so as to follow the change in the allocation of resource blocks used by the LTE system, or may be executed when the frequency of the intermodulation wave changes.

(Modification example for determining whether demodulation is possible based on signal strength)
When the subcarrier and the intermodulation wave overlap, the demodulator 35 performs demodulation by excluding the corresponding subcarrier, but when there are a plurality of weak intermodulation waves, the signal can be demodulated without any problem. The plurality of subcarriers are excluded, and as a result, there is a possibility that all data cannot be demodulated. In order to avoid this, it is this modification that determines whether or not demodulation is possible based on the signal strength. Detailed description will be given below.

  The signal strength of the carrier can be represented by a value called RSSI (Received Signal Strength Indicator), and its unit is [dB] or [dBm]. FIG. 9 is a diagram illustrating a case where there is a difference in signal strength between subcarriers used by the ITS system and subcarriers used by the LTE system. The example of FIG. 9 shows that the subcarrier used by the ITS system has a signal strength of d1 [dBm], and the subcarrier used by the LTE system has a signal strength of d2 [dBm].

  The reception unit 34 acquires the signal strength of the subcarrier used by the ITS system, and the measured signal strength is transmitted to the demodulation unit 35. Similarly, the reception unit 34 also measures the signal strength of the subcarriers used by the LTE system, and the signal strength is transmitted to the interference wave detection unit 33 via the sensing unit 32. Here, when the interference wave detection unit 33 detects the intermodulation wave, the signal strength of the corresponding LTE system is transmitted to the demodulation unit 35 together with information on the frequency of the intermodulation wave.

  The demodulator 35 holds conditions regarding signal strength. The condition relating to the signal strength can be set as “when d1−d2 is 10 dB or less”, for example. The demodulator 35 receives the signal strength before executing the demodulation processing in step S14, determines whether the signal strength of the intermodulation wave satisfies the condition, and determines whether demodulation is possible.

  By doing so, processing can be performed while ignoring weak intermodulation waves that do not affect the communication of the ITS system. When an LTE mobile phone is used inside an automobile, the signal strength in the upstream band is strong, so interference occurs in data demodulation due to interference, but there is no failure when used outside the vehicle. Can be considered. In such a case, it is effective to determine whether or not demodulation is possible based on the signal strength.

(Modified example of determining whether demodulation is possible or not by error detection)
In addition to determining whether to demodulate based on the signal strength, this modification is an example in which subcarriers are excluded only when data is actually demodulated and cannot be demodulated normally.

  FIG. 10 is a flowchart according to this modification. Except for the processing between steps S13 to S14, it is the same as the flowchart of FIG. After identifying the intermodulation wave in step S13, the demodulation unit 35 performs a process of demodulating all the subcarriers (S13a). As a result, if the data can be correctly demodulated, the process is continued. If an error occurs during demodulation, the interfering subcarrier is excluded and demodulated (S13b).

  The normality / abnormality of the demodulation may be determined based on an error detection result using a hash function, for example, when the received power is high but the error does not occur so much. If error correction is impossible as a result of error correction using an error correction code such as a code, it may be determined as abnormal.

  Further, an error rate at the time of demodulation may be calculated, and it may be determined as abnormal when a predetermined value is exceeded. In this case, for example, in a demodulation process of a plurality of symbols, when a predetermined error rate is continuously exceeded, an abnormality may be set, or an average error rate may be used.

  With this configuration, it is possible to perform an operation of excluding subcarriers only when an intermodulation wave actually affects demodulation, and processing overhead is reduced.

  The above embodiment is merely an example, and the present invention can be implemented with appropriate modifications within a range not departing from the gist thereof. For example, the flowchart shown above exemplifies the operation, and all the processes may not be performed in the order illustrated, or unnecessary processes may be skipped. For example, when the resource block being used has not changed, it is not necessary to perform frequency calculation of the interference wave again, and it is not always necessary to check whether all subcarriers can be demodulated.

  Further, the radio system that causes the intermodulation wave may be other than the LTE system as long as it generates the intermodulation wave in a specific narrow band as described in the example of the embodiment. In that case, the same effect as this embodiment can be obtained by applying an algorithm for generating an interference wave to this embodiment.

In this embodiment, an ITS system using OFDM as a modulation scheme is exemplified as an interfered radio system. However, any other modulation scheme may be used as long as it is a multicarrier modulation scheme. For example, OFDMA (Orthogonal Frequency Division Multiple Access: Orthogonal Frequency
Division Multiple Access) may be used.

3 Radio Receiver 31 Antenna 32 Sensing Unit 33 Interference Wave Detection Unit 34 Reception Unit 35 Demodulation Unit 36 Information Processing Unit

Claims (6)

A radio receiver for receiving and demodulating a first radio signal transmitted by a multicarrier modulation method,
Receiving means for receiving the first radio signal and a second radio signal transmitted in a frequency band near the frequency band in which the first radio signal is transmitted;
Sensing means for detecting a carrier having a signal strength of a predetermined value or more from the second radio signal received by the receiving means;
Interference wave detecting means for calculating a frequency band of an intermodulation wave generated by the detected carrier wave;
When the frequency band of the intermodulation wave is included in the frequency band in which the first radio signal is transmitted, the carrier wave including the frequency band of the intermodulation wave among the carriers included in the first radio signal And demodulating means for demodulating the first radio signal,
A wireless receiver comprising: The demodulating means demodulates the first radio signal by excluding a carrier wave including a frequency band of the intermodulation wave when the signal strength of the carrier wave included in the second radio signal satisfies a predetermined condition. The wireless receiver according to claim 1. The demodulating means further includes means for detecting an error generated during demodulation, and when it is determined that the demodulation is not performed normally, the first demodulator excludes the carrier wave including the frequency band of the intermodulation wave. The radio receiver according to claim 1, wherein the radio signal is demodulated. The radio receiver according to any one of claims 1 to 3, wherein the modulation method of the first radio signal is OFDM and the modulation method of the second radio signal is SC-FDMA. The interference wave detecting means is expressed by equations (1) and (2), where a is a carrier frequency detected by the sensing means, and b is a center frequency of a frequency band used for transmission of the second radio signal. The expressed frequency A, B is calculated as the frequency of the intermodulation wave. The radio receiver according to any one of claims 1 to 4.
A = 4b-3a Formula (1)
B = 3a-2b Formula (2) A radio reception method for receiving and demodulating a first radio signal transmitted by a multicarrier modulation method,
Receiving the first radio signal and a second radio signal transmitted in a frequency band near the frequency band in which the first radio signal is transmitted;
From the received second radio signal, a carrier wave having a signal strength of a predetermined value or more is detected,
Calculating a frequency band of an intermodulation wave generated by the detected carrier wave;
When the frequency band of the intermodulation wave is included in the frequency band in which the first radio signal is transmitted, the carrier wave including the frequency band of the intermodulation wave among the carriers included in the first radio signal A radio receiving method, wherein the first radio signal is demodulated without the above.

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