Interference cancellation device, control circuit, storage medium, and interference cancellation method

Abstract

The present invention provides an interference cancellation device (1) capable of suppressing deterioration due to noise enhancement. This interference cancellation device comprises: a data symbol extraction unit (11) that outputs a data symbol signal (101); a null symbol extraction unit (12) that outputs a null symbol signal (102); a data symbol power calculation unit (14) that calculates a data symbol power estimated value (104); a null symbol spectrum calculation unit (15) that calculates a null symbol spectrum (105); a received signal spectrum calculation unit (16) that calculates a received signal spectrum (106); an interference center frequency estimation unit (17) that outputs an interference center frequency estimated value (107) and an estimated interference bandwidth (108); and an interference cancellation unit (18) that suppresses deterioration due to noise enhancement according to the ratio between interference power included in the null symbol spectrum (105) and residual noise power included in the received signal spectrum after interference cancellation.

Description

Interference cancellation device, control circuit, storage medium, and interference cancellation method

[0001] The present disclosure relates to an interference cancellation device, a control circuit, a storage medium, and an interference cancellation method for canceling interference from a received signal.

[0002] Conventionally, interference removal using intermittent symbol transmission has been used as a method for removing interference from a received signal in a receiving device. In interference removal using intermittent symbol transmission, a transmitting device transmits a signal by inserting non-transmission intervals, so-called null symbols, between transmitted symbols. The receiving device removes interference by subtracting from the received signal an interference replica signal that regenerates interference superimposed on the data portion from interference components superimposed on the null symbol portion of the received signal. For example, Patent Document 1 discloses a technology that improves the efficiency of interference suppression and reduces the number of iterations by varying a weighting coefficient that is multiplied by the interference replica according to the remaining interference power for each iteration.

[0003] Furthermore, Patent Document 2 discloses a technology in which a null symbol spectrum is passed through a plurality of band-limiting filters having a passband defined for a system bandwidth, which is the frequency band through which a received signal is transmitted, and the defined frequencies are shifted by defined amounts, and the null symbol spectrum after passing through the filters is converted from a frequency domain signal to a time domain signal by an Inverse Fast Fourier Transform (IFFT), and the difference between a time domain interference replica signal and the received signal is calculated, thereby obtaining residual interference noise power after multiple interferences have been removed and estimating an interference center frequency.

[0004] Patent No. 6746029 Patent No. 7004877

[0005] When the technology described in Patent Document 1 is applied to an interference cancellation method using intermittent symbol transmission, interference cancellation is performed by directly subtracting the interference replica signal from the received signal, regardless of the ratio between the interference power component and the noise power component contained in the interference replica signal. In this case, if the interference power is small compared to the noise signal in the interference replica signal, the degradation due to noise enhancement becomes more significant than the improvement effect of interference cancellation. However, Patent Document 1 does not disclose how to suppress the degradation due to noise enhancement.

[0006] Furthermore, in the method for estimating the center frequency of an interference signal described in Patent Document 2, a null symbol spectrum is passed through a plurality of band-limiting filters having defined passbands, and the null symbol spectrum that has passed through the filters is converted from the frequency domain to the time domain by IFFT. In this case, if the conversion from the frequency domain to the time domain is performed simultaneously in parallel to reduce delay time, a problem arises in that the number of IFFT circuits required is equal to the number of parallel filters, which increases the circuit size.

[0007] The present disclosure has been made in view of the above, and aims to provide an interference removal device that can suppress degradation due to noise enhancement.

[0008] and a reception signal spectrum calculation unit that calculates a reception signal spectrum from the reception signal. The present disclosure provides a reception signal spectrum calculation unit that calculates a reception signal spectrum from the reception signal. The present disclosure provides a reception signal spectrum calculation unit that calculates a reception signal spectrum from the reception signal. The present disclosure provides a reception signal spectrum calculation unit that calculates a reception signal spectrum from the reception signal. The present disclosure provides a reception signal spectrum calculation unit that calculates a reception signal spectrum from the reception signal. The present disclosure provides an interference center frequency estimation unit that estimates a center frequency and a bandwidth of an interference signal using the data symbol power estimate, the null symbol spectrum, and the reception signal spectrum, and outputs an interference center frequency estimate and an estimated interference bandwidth. The present disclosure provides an interference cancellation unit that suppresses degradation due to noise emphasis by combining, for each frequency, spectral components in an interference band and spectral components in a band not containing interference, in accordance with a ratio between the interference power included in the null symbol spectrum and the residual noise power included in the reception signal spectrum after interference cancellation.

[0009] The interference removal device of the present disclosure has the effect of suppressing degradation due to noise enhancement.

[0010] FIG. 1 is a block diagram showing an example of the configuration of an interference cancellation device according to an embodiment; FIG. 2 is a flowchart showing the operation of the interference cancellation device according to an embodiment; FIG. 3 is a block diagram showing an example of the configuration of an interference center frequency estimation unit according to an embodiment; FIG. 4 is a flowchart showing the operation of the interference center frequency estimation unit according to an embodiment; FIG. 5 is a diagram showing the relationship between each frequency band in the spectrum regeneration unit according to an embodiment and a system frequency;

[0011] Hereinafter, an interference cancellation device, a control circuit, a storage medium, and an interference cancellation method according to embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0012] 1 is a block diagram showing an example of the configuration of an interference cancellation device 1 according to this embodiment. The interference cancellation device 1 is a device mounted on a receiving device (not shown) or the like. The interference cancellation device 1 removes interference added in a propagation path between a transmitting device (not shown) that is the signal source and the receiving device from a received signal 100 that is a signal received by the receiving device. In this embodiment, the transmitting device inserts null symbols to data symbols in a one-to-one ratio in the transmitted signal, that is, inserts data symbols and null symbols alternately. In the received signal 100 received by the receiving device, null symbols are inserted between data symbols.

[0013] The following describes the configuration and operation of the interference cancellation device 1. As shown in Fig. 1, the interference cancellation device 1 includes a data symbol extraction unit 11, a null symbol extraction unit 12, a null symbol power calculation unit 13, a data symbol power calculation unit 14, a null symbol spectrum calculation unit 15, a received signal spectrum calculation unit 16, an interference center frequency estimation unit 17, and an interference cancellation unit 18. Fig. 2 is a flowchart showing the operation of the interference cancellation device 1 according to this embodiment.

[0014] The data symbol extractor 11 extracts only the data symbol portion from the received signal 100 in accordance with the timing of the data symbol (step S11). The data symbol extractor 11 outputs the extracted data symbol portion as a data symbol signal 101.

[0015] The null symbol extractor 12 extracts only the null symbol portion from the received signal 100 in synchronization with the null symbol timing (step S12). The null symbol extractor 12 outputs the extracted null symbol portion as a null symbol signal 102.

[0016] The null symbol power calculation unit 13 calculates the power P of the null symbol signal 102. １ (Step S13). The l-th signal of the null symbol signal 102 is calculated as r Ｎ (l), then the power P １ is expressed as in equation (1): In equation (1), L is the number of symbols used in power calculation.

[0017]

[0018] Here, the null symbol signal 102 contains interference and noise. That is, if I is the interference power and N is the noise power, then P １ = I + N. The null symbol power calculation unit 13 calculates P １ = null symbol power estimate 103, and calculate null symbol power estimate 103.

[0019] The data symbol power calculation unit 14 calculates the power P ０, and the power P １ (Step S14) where the data symbol signal 101 includes data symbols, interference, and noise. That is, if D is the transmission data symbol power, then P ０ = D + I + N. Therefore, the data symbol power calculation unit 14 calculates D = P ０ -P １ = data symbol power estimate 104, and calculate the data symbol power estimate 104 as the data symbol power included in the data symbol signal 101. The k-th symbol of the data symbol signal 101 is expressed as r Ｄ (k), the power P ０ is expressed as in equation (2): In equation (2), K is the number of symbols used in power calculation.

[0020]

[0021] The null symbol spectrum calculation unit 15 calculates the null symbol spectrum 105 from the null symbol signal 102 (step S15). The null symbol spectrum calculation unit 15 calculates the null symbol spectrum 105 using, for example, a fast Fourier transform (FFT). The null symbol power calculation unit 13, the data symbol power calculation unit 14, and the null symbol spectrum calculation unit 15 may be simply referred to as calculation units. One calculation unit may also perform multiple of the above calculations.

[0022] The received signal spectrum calculation unit 16 calculates the received signal spectrum 106 from the received signal 100 (step S16). The received signal spectrum calculation unit 16 calculates the received signal spectrum 106 using, for example, a fast Fourier transform (FFT).

[0023] The interference center frequency estimation unit 17 estimates the center frequency and bandwidth of the interference signal using the data symbol power estimate 104, the null symbol spectrum 105, and the received signal spectrum 106, and calculates the interference center frequency estimate 107 and the estimated interference bandwidth 108 (step S17). The interference center frequency estimation unit 17 outputs the interference center frequency estimate 107 and the estimated interference bandwidth 108.

[0024] The interference canceller 18 cancels interference from the received signal 100 using the data symbol power estimate 104, the null symbol spectrum 105, the received signal spectrum 106, the interference center frequency estimate 107, and the estimated interference bandwidth 108 (step S18). The interference canceller 18 outputs an interference-canceled received signal 109, which is a signal obtained by removing interference from the received signal 100. In this embodiment, the interference canceller 18 uses the received signal spectrum 106, the data symbol power estimate 104, the null symbol spectrum 105, the interference center frequency estimate 107, and the estimated interference bandwidth 108 to combine, for each frequency, spectral components in the interference band and spectral components in a band not containing interference in accordance with the ratio between the interference power included in the null symbol spectrum 105 and the residual noise power included in the received signal spectrum after interference cancellation, thereby suppressing degradation due to noise emphasis.

[0025] Next, a detailed configuration and operation of the interference center frequency estimator 17 included in the interference removal device 1 will be described. Fig. 3 is a block diagram showing an example configuration of the interference center frequency estimator 17 according to this embodiment. As shown in Fig. 3, the interference center frequency estimator 17 includes spectrum regenerators 21a, 21b, 21c, and 21d, post-interference-removal data symbol power calculators 22a, 22b, 22c, and 22d, data symbol power subtractors 23a, 23b, 23c, and 23d, an interference bandwidth calculator 24, and an estimation unit 25. Fig. 4 is a flowchart showing the operation of the interference center frequency estimator 17 according to this embodiment.

[0026] The spectrum regeneration units 21a to 21d copy four different frequency components to the received signal spectrum 106, thereby regenerating the spectrum (step S21). The source and destination frequency components of the spectrum regeneration units 21a to 21d are all 50% of the system bandwidth, but are in different frequency bands. Each source and destination frequency component of the spectrum regeneration units 21a to 21d overlaps with the adjacent frequency band by 25% of the system bandwidth.

[0027] FIG. 5 shows the frequency bands F0 to F3 and the system frequency F in the spectrum regeneration units 21a to 21d according to this embodiment. ｓ 5 is a diagram showing the relationship between F ｓ is the system bandwidth, and F0 band, F1 band, F2 band, and F3 band are F ｓ Received signal spectrum 106 has F0 band spectrum 501 in the F0 band, F1 band spectrum 502 in the F1 band, F2 band spectrum 503 in the F2 band, and F3 band spectrum 504 in the F3 band.

[0028] The spectrum regeneration unit 21a inverts the sign of the F2 band spectrum 503 and copies it to the F0 band, and inverts the sign of the F1 band spectrum 502 and copies it to the F3 band. Furthermore, the spectrum regeneration unit 21a inverts the sign of the F2 band spectrum 503 in the copied frequency spectrum and adds it to the F0 band spectrum 501 in the copied frequency spectrum. Similarly, the spectrum regeneration unit 21a inverts the sign of the F1 band spectrum 502 in the copied frequency spectrum and adds it to the F3 band spectrum 504 in the copied frequency spectrum. After the above operations, the spectrum regeneration unit 21a outputs the interference-removed data symbol spectrum 201a consisting only of spectral components in the F0 band and F3 band. The interference-removed data symbol spectrum 201a is output as R ｒａ Let it be expressed as (n), where n is the frequency number.

[0029] The spectrum regeneration unit 21b inverts the sign of the F2 band spectrum 503 and copies it to the F0 band, and inverts the sign of the F3 band spectrum 504 and copies it to the F1 band. Furthermore, the spectrum regeneration unit 21b inverts the sign of the F2 band spectrum 503 in the copied frequency spectrum and adds it to the F0 band spectrum 501 in the copied frequency spectrum. Similarly, the spectrum regeneration unit 21b inverts the sign of the F1 band spectrum 502 in the copied frequency spectrum and adds it to the F3 band spectrum 504 in the copied frequency spectrum. After the above operations, the spectrum regeneration unit 21b outputs the interference-removed data symbol spectrum 201b consisting only of spectral components in the F0 band and F3 band. The interference-removed data symbol spectrum 201b is output as R ｒｂ Let it be represented as (n).

[0030] The spectrum regeneration unit 21c inverts the sign of the F0 band spectrum 501 and copies it to the F2 band, and determines the sign of the F3 band spectrum 504 and copies it to the F1 band. Furthermore, the spectrum regeneration unit 21c inverts the sign of the F2 band spectrum 503 in the copied frequency spectrum and adds it to the F0 band spectrum 501 in the copied frequency spectrum. Similarly, the spectrum regeneration unit 21c inverts the sign of the F1 band spectrum 502 in the copied frequency spectrum and adds it to the F3 band spectrum 504 in the copied frequency spectrum. After the above operations, the spectrum regeneration unit 21c outputs the interference-removed data symbol spectrum 201c consisting only of spectral components in the F0 band and F3 band. The interference-removed data symbol spectrum 201c is output as R ｒｃ Let it be represented as (n).

[0031] The spectrum regeneration unit 21d inverts the sign of the F0 band spectrum 501 and copies it to the F2 band, and determines the sign of the F1 band spectrum 502 and copies it to the F3 band. Furthermore, the spectrum regeneration unit 21d inverts the sign of the F2 band spectrum 503 in the copied frequency spectrum and adds it to the F0 band spectrum 501 in the copied frequency spectrum. Similarly, the spectrum regeneration unit 21d inverts the sign of the F1 band spectrum 502 in the copied frequency spectrum and adds it to the F3 band spectrum 504 in the copied frequency spectrum. After the above operations, the spectrum regeneration unit 21d outputs the interference-canceled data symbol spectrum 201d consisting only of spectral components in the F0 band and F3 band. The interference-canceled data symbol spectrum 201d is output as R ｒｄ Let it be represented as (n).

[0032] The post-interference-canceled data symbol power calculation units 22a, 22b, 22c, and 22d calculate and output the power of the post-interference-canceled data symbol spectra 201a, 201b, 201c, and 201d as post-interference-canceled data symbol powers 202a, 202b, 202c, and 202d (step S22). ｒａ , P ｒｂ , P ｒｃ , P ｒｄ Then, the post-interference-removal data symbol power calculation units 22a, 22b, 22c, and 22d perform calculations using equation (3).

[0033]

[0034] The data symbol power subtractors 23a, 23b, 23c, and 23d respectively subtract P ｒａ , P ｒｂ , P ｒｃ , P ｒｄ By subtracting the data symbol power estimate 104, i.e., the transmitted data symbol power D, from the residual interference noise power values ​​203a, 203b, 203c, and 203d (step S23).

[0035] The interference bandwidth calculation unit 24 determines and marks any null symbol spectrum 105 that exceeds a predefined threshold as an interference band. For example, assume that the shape of the null symbol spectrum 105 is as shown in FIG. 6 . FIG. 6 is a diagram showing an example of the null symbol spectrum 105 calculated by the null symbol spectrum calculation unit 15 of the interference removal device 1 according to this embodiment. The null symbol spectrum 105 includes interference 601, an image 602 of the interference 601, and noise 603. The interference bandwidth calculation unit 24 determines and marks any null symbol spectrum 105 that exceeds a predefined threshold 604 as an interference band 605. In this case, the interference band 605 marked by the interference bandwidth calculation unit 24 is the interference 601 and the image 602, and is twice the interference bandwidth of the actual interference 601. Therefore, the interference bandwidth calculation unit 24 calculates half the interference bandwidth of the interference band 605 as the estimated interference bandwidth 108 of the actual interference 601 (step S24).

[0036] In this way, in the interference center frequency estimation unit 17, the interference bandwidth calculation unit 24 compares the null symbol spectrum 105 with the specified threshold 604 when calculating the interference center frequency estimate 107, and halves the total bandwidth of the parts exceeding the threshold 604 to obtain the estimated interference bandwidth 108 of the interference 601. The interference bandwidth calculation unit 24 excludes the influence of the image 602 on the interference 601 in calculating the estimated interference bandwidth 108.

[0037] The estimation unit 25 estimates the interference center frequency using the residual interference noise power values ​​203a to 203d, the estimated interference bandwidth 108, and the null symbol spectrum 105, and calculates the interference center frequency estimate value 107 (step S25). The estimation unit 25 can calculate the interference center frequency estimate value 107 by, for example, the same operation as the estimation unit described in the aforementioned Patent Document 2.

[0038] In this way, the interference center frequency estimation unit 17 uses the data symbol power estimate value 104, the received signal spectrum 106, and the null symbol spectrum 105 to utilize the characteristic that the same frequency spectrum is repeated in the frequency direction in the received signal spectrum 106, which is a frequency domain signal of a time signal sequence composed of null symbols and data symbols, and copies the spectral components of signal bands other than the specified frequency band to the specified frequency band within the received signal spectrum 106, thereby removing interference without regenerating the interference replica signal.

[0039] Next, a detailed configuration and operation of the interference removal unit 18 included in the interference removal device 1 will be described. Fig. 7 is a block diagram showing an example configuration of the interference removal unit 18 according to this embodiment. As shown in Fig. 7, the interference removal unit 18 includes a spectrum regeneration unit 31, a time domain conversion unit 32, a residual noise estimation unit 33, and a weighting coefficient calculation unit 34. Fig. 8 is a flowchart showing the operation of the interference removal unit 18 according to this embodiment.

[0040] The spectrum regeneration unit 31 performs spectrum regeneration using the received signal spectrum 106, the interference center frequency estimate 107, and the estimated interference bandwidth 108 to generate the interference-removed data symbol spectrum 302 (step S31). The interference-removed data symbol spectrum 302 is a value obtained by weighting and adding the spectrum of the copy source band and the interference band in the received signal spectrum 106 for the interference band, and is the spectral value of the received signal spectrum 106 itself for the non-interference bands other than the interference band.

[0041] 9 is a diagram showing an example of the band configuration of the received signal spectrum 106 according to this embodiment. The received signal spectrum 106 is composed of an interference band 401, a non-interference band 402, and a copy source band 403. The interference band 401 is a frequency band within the received signal spectrum 106 calculated from the interference center frequency estimate 107 and the estimated interference bandwidth 108, and includes a lower frequency F ｌ to the upper frequency F ｈ The non-interference band 402 is a frequency band other than the interference band 401. The copy source band 403 is a frequency band between the system frequency Fｓ Then, the lower frequency F ｌ +F ｓ / 2 to the upper frequency F ｈ +F ｓ The frequency band is the system frequency F ｓ The following values ​​are calculated as the system frequency F ｓ If it exceeds the system frequency F ｓ The remainder value is obtained by

[0042] If the received signal spectrum 106 is R(n) and the interference-removed data symbol spectrum 302 is R(∼)(n), the spectrum regenerator 31 replaces the spectrum of the interference band 401 using equation (4), where n is the frequency number.

[0043]

[0044] In the specification, it is not possible to express the state where ~ is added above R, so here, the state where ~ is added above R will be expressed as R(~).

[0045] Here, W(n) is the weighting coefficient 301 by which the frequency domain signal is multiplied. Since W(n) is calculated based on the output of the spectrum regeneration unit 31, the initial value is set to W(n) = 1 for all n. However, this initial value setting is not necessarily required.

[0046] The time domain transform unit 32 converts the post-interference-canceled data symbol spectrum 302 from a frequency domain signal to a time domain signal after null symbol removal, generating post-interference-canceled received signal 109 converted into a time domain signal (step S32). As a method of null symbol removal, the time domain transform unit 32 inverts the sign of F2 band spectrum 503 in post-interference-canceled data symbol spectrum 302 and adds it to F0 band spectrum 501 in post-interference-canceled data symbol spectrum 302. Similarly, as a method of null symbol removal, the time domain transform unit 32 inverts the sign of F1 band spectrum 502 in post-interference-canceled data symbol spectrum 302 and adds it to F3 band spectrum 504 in post-interference-canceled data symbol spectrum 302. The frequency data after the above operations consists only of spectral components in the F0 band and F3 band. The time domain transform unit 32 uses, for example, an inverse fast Fourier transform (IFFT) to transform to the time domain.

[0047] The residual noise estimator 33 calculates the residual noise power 303 using the interference-removed data symbol spectrum 302 and the data symbol power estimate 104 (step S33). First, the residual noise estimator 33 calculates the power P ｒ０ (n) is calculated by equation (5). The power P of the data symbol spectrum 302 after interference cancellation ｒ０ Ideally, (n) is the sum of the transmission data symbol power D at each frequency and the residual noise contained in the signal band after interference removal. Note that in equation (5), n is the frequency number.

[0048]

[0049] The residual noise estimation unit 33 further estimates the power P ｒ０ By subtracting the power per frequency of the data symbol power estimate 104 from (n) as shown in equation (6), N ｒ (n) is calculated. In equation (6), B is the signal bandwidth.

[0050] Nｒ (n) = P ｒ０ (n)-D / B...(6)

[0051] The weighting factor calculation unit 34 calculates the weighting factor 301 using the null symbol spectrum 105 and the residual noise power 303 (step S34). Since the null symbol is composed of an interference signal and a noise signal, the null symbol spectrum 105 is a one-dimensional vector with n as the frequency number. ｎｕｌｌ (n), the null symbol power spectrum is expressed by equation (7). Note that the null symbol power spectrum is calculated by subtracting the interference power I ｓｐ (n) and noise power N ｓｐ (n), that is, I ｓｐ (n) + N ｓｐ (n).

[0052] I ｓｐ (n) + N ｓｐ (n) = |R ｎｕｌｌ (n) | ２ …(7)

[0053] Here, the weighting coefficient 301 is a weighting coefficient for avoiding unnecessary noise emphasis in the spectrum regeneration unit 31. The weighting coefficient has the following characteristics: ｓｐ (n) is the interference power I ｓｐ (n), the weighting factor approaches 0 because removing the interference signal adds unnecessary noise. ｓｐ (n) is the interference power I ｓｐ When I is much smaller than (n), complete elimination of the interference signal becomes important, so the weighting coefficient approaches 1. Taking this characteristic into consideration, the weighting coefficient 301 is calculated as shown in equation (8). ｅｓｔ (n) is the estimated interference power I calculated by subtracting the residual noise power 303 from the null symbol power spectrum. ｅｓｔ (n) = I ｓｐ (n) + N ｓｐ (n)-N ｒ (n).

[0054] W(n) = I ｅｓｔ (n) / (I ｓｐ(n) + N ｓｐ (n)) ... (8)

[0055] In this way, the interference removal unit 18 uses the data symbol power estimate 104, the received signal spectrum 106, the null symbol spectrum 105, the interference center frequency estimate 107, and the estimated interference bandwidth 108 to take advantage of the feature that the same frequency spectrum is repeated in the frequency direction in the received signal spectrum 106, which is a frequency domain signal of a time signal sequence composed of null symbols and data symbols, and copies the spectral components of signal bands other than the interference band to the interference band identified from the interference center frequency estimate 107 and the estimated interference bandwidth 108 within the received signal spectrum 106, thereby removing interference without regenerating the interference replica signal.

[0056] As described above, according to this embodiment, the interference cancellation device 1 utilizes the fact that the frequency spectrum of a time-domain symbol sequence including null symbols and data symbols has redundancy that is repeated in the frequency direction, thereby making it possible to cancel interference without regenerating the interfering signal and reducing the circuit scale of the interference cancellation device 1. As a result, the interference cancellation device 1 can achieve a device with the same interference cancellation function with a smaller circuit scale.

[0057] In addition, by setting the weighting coefficient 301 for each frequency, the interference cancellation device 1 can simultaneously avoid unnecessary noise enhancement at frequencies with a low INR (Interference to Noise power Ratio) and reliably cancel interference at frequencies with a high INR. This allows the interference cancellation device 1 to efficiently cancel interference signals contained in the received signal 100 and reduce degradation of reception quality, for example, bit error rate. The interference cancellation device 1 can suppress degradation due to noise enhancement. The interference cancellation device 1 can also minimize degradation due to noise enhancement.

[0058] The reduction in circuit scale and improvement in interference resistance achieved by the interference removal device 1 of this embodiment makes it possible to realize stable wireless communication against various interference spectra on the frequency axis at lower cost.

[0059] Next, a description will be given of the hardware configuration of the interference cancellation device 1. In the interference cancellation device 1, the data symbol extraction unit 11, the null symbol extraction unit 12, the null symbol power calculation unit 13, the data symbol power calculation unit 14, the null symbol spectrum calculation unit 15, the received signal spectrum calculation unit 16, the interference center frequency estimation unit 17, and the interference cancellation unit 18 are realized by processing circuits. The processing circuits may be a processor and memory that executes a program stored in a memory, or may be dedicated hardware. The processing circuits are also called control circuits.

[0060] FIG. 10 is a diagram showing an example of the configuration of a processing circuit 90 when the processing circuit for implementing the interference removal device 1 according to this embodiment is implemented by a processor 91 and a memory 92. The processing circuit 90 shown in FIG. 10 is a control circuit and includes a processor 91 and a memory 92. When the processing circuit 90 is configured with the processor 91 and the memory 92, each function of the processing circuit 90 is implemented by software, firmware, or a combination of software and firmware. The software or firmware is written as a program and stored in the memory 92. The processing circuit 90 realizes each function by having the processor 91 read and execute the program stored in the memory 92. That is, the processing circuit 90 includes the memory 92 for storing a program that results in the processing of the interference removal device 1 being executed. This program can also be said to be a program that causes the interference removal device 1 to execute each function implemented by the processing circuit 90. This program may be provided by a storage medium on which the program is stored, or by other means such as a communication medium.

[0061] The program includes a first step in which a data symbol extractor 11 extracts a data symbol portion from a received signal 100 in which null symbols have been inserted into the data symbols, and outputs a data symbol signal 101; a second step in which a null symbol extractor 12 extracts a null symbol portion from the received signal 100, and outputs a null symbol signal 102; a third step in which a null symbol power calculator 13 calculates a null symbol power estimate 103 indicating the power of the null symbol signal 102; a fourth step in which a data symbol power calculator 14 calculates a data symbol power estimate 104 indicating the power of the data symbol signal 101; and a fourth step in which a null symbol spectrum calculator 15 calculates a null symbol portion from the null symbol signal 102. a fifth step of calculating a symbol spectrum 105; a sixth step of the received signal spectrum calculation unit 16 calculating a received signal spectrum 106 from the received signal 100; a seventh step of the interference center frequency estimation unit 17 estimating the center frequency and bandwidth of the interference signal using the data symbol power estimate 104, the null symbol spectrum 105, and the received signal spectrum 106, and outputting an interference center frequency estimate 107 and an estimated interference bandwidth 108; and a seventh step of the interference removal unit 18 estimating the interference power I included in the null symbol spectrum 105 using the received signal spectrum 106, the data symbol power estimate 104, the null symbol spectrum 105, the interference center frequency estimate 107, and the estimated interference bandwidth 108. ｓｐ and an eighth step of suppressing degradation due to noise emphasis by combining, for each frequency, the spectral components in the interference band with the spectral components in a band not containing interference, in accordance with the ratio of (n) to the residual noise power 303 contained in the received signal spectrum after interference removal.

[0062] Here, the processor 91 may be a CPU (Central Processing Unit), a processing device, an arithmetic device, a microprocessor, a microcomputer, or a DSP (Digital Signal Processor), etc. The memory 92 may be, for example, a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable ROM), or an EEPROM (Electrically EPROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a minidisk, or a DVD (Digital Versatile Disc).

[0063] 11 is a diagram showing an example in which the processing circuit 93 that realizes the interference cancellation device 1 according to this embodiment is configured with dedicated hardware. When the processing circuit 93 is configured with dedicated hardware, the processing circuit 93 shown in FIG. 11 corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. Each function of the interference cancellation device 1 may be realized by the processing circuit 93 separately, or all functions may be realized collectively by the processing circuit 93.

[0064] It should be noted that some of the functions of the interference removal device 1 may be realized by dedicated hardware and some by software or firmware. In this way, the processing circuit can realize each of the above-described functions by dedicated hardware, software, firmware, or a combination of these.

[0065] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, and parts of the configurations may be omitted or modified without departing from the spirit of the invention.

[0066] 1 Interference removal device, 11 Data symbol extraction unit, 12 Null symbol extraction unit, 13 Null symbol power calculation unit, 14 Data symbol power calculation unit, 15 Null symbol spectrum calculation unit, 16 Received signal spectrum calculation unit, 17 Interference center frequency estimation unit, 18 Interference removal unit, 21a to 21d, 31 Spectral regeneration unit, 22a to 22d Data symbol power calculation unit after interference removal, 23a to 23d Data symbol power subtraction unit, 24 Interference bandwidth calculation unit, 25 Estimation unit, 32 Time domain conversion unit, 33 Residual noise estimation unit, 34 Weighting coefficient calculation unit, 90, 93 Processing circuit, 91 Processor, 92 Memory.

Claims

1. An interference cancellation device comprising: a data symbol extraction unit that outputs a data symbol signal extracted from a received signal in which null symbols have been inserted into data symbols; a null symbol extraction unit that outputs a null symbol signal extracted from the received signal; a calculation unit that calculates a data symbol power estimate indicating the power of the data symbol signal and a null symbol spectrum from the null symbol signal; a received signal spectrum calculation unit that calculates the received signal spectrum from the received signal; an interference center frequency estimation unit that estimates a center frequency and bandwidth of an interfering signal using the data symbol power estimate, the null symbol spectrum, and the received signal spectrum, and outputs an interference center frequency estimate and an estimated interference bandwidth; and an interference cancellation unit that suppresses degradation due to noise emphasis by combining, for each frequency, spectral components in an interference band and spectral components in a band not containing interference, in accordance with the ratio between the interference power included in the null symbol spectrum and the residual noise power included in the received signal spectrum after interference cancellation.

2. The interference removal device according to claim 1, characterized in that the interference center frequency estimation unit uses the data symbol power estimate, the received signal spectrum, and the null symbol spectrum to utilize a feature in which the same frequency spectrum is repeated in the frequency direction in the received signal spectrum, which is a frequency domain signal of a time signal sequence composed of the null symbols and the data symbols, to copy spectral components of signal bands other than a specified frequency band to a specified frequency band within the received signal spectrum, thereby removing interference without regenerating an interference replica signal.

3. The interference removal device according to claim 1 or 2, characterized in that the interference removal unit uses the data symbol power estimate, the received signal spectrum, the null symbol spectrum, the interference center frequency estimate, and the estimated interference bandwidth to take advantage of a feature in which the same frequency spectrum is repeated in the frequency direction in the received signal spectrum, which is a frequency domain signal of a time signal sequence composed of the null symbols and the data symbols, to copy spectral components of signal bands other than the interference band to an interference band within the received signal spectrum that is identified from the interference center frequency estimate and the estimated interference bandwidth, thereby removing interference without regenerating an interference replica signal.

4. A control circuit for controlling an interference cancellation device, comprising: extracting a data symbol portion from a received signal in which null symbols have been inserted into data symbols, and outputting a data symbol signal; extracting a null symbol portion from the received signal, and outputting a null symbol signal; calculating a null symbol power estimate indicating the power of the null symbol signal; calculating a data symbol power estimate indicating the power of the data symbol signal; calculating a null symbol spectrum from the null symbol signal; calculating a received signal spectrum from the received signal; estimating a center frequency and bandwidth of an interfering signal using the data symbol power estimate, the null symbol spectrum, and the received signal spectrum, and outputting an interference center frequency estimate and an estimated interference bandwidth; suppressing degradation due to noise emphasis by combining, for each frequency, spectral components within an interference band and spectral components within a band not containing interference, using the received signal spectrum, the data symbol power estimate, the null symbol spectrum, the interference center frequency estimate, and the estimated interference bandwidth, in accordance with the ratio between the interference power contained in the null symbol spectrum and the residual noise power contained in the received signal spectrum after interference cancellation.

5. A storage medium storing a program for controlling an interference removal device, wherein the program: extracts a data symbol portion from a received signal in which null symbols have been inserted into data symbols, and outputs a data symbol signal; extracts a null symbol portion from the received signal, and outputs a null symbol signal; calculates a null symbol power estimate indicating the power of the null symbol signal; calculates a data symbol power estimate indicating the power of the data symbol signal; calculates a null symbol spectrum from the null symbol signal; calculates a received signal spectrum from the received signal; estimates a center frequency and bandwidth of an interference signal using the data symbol power estimate, the null symbol spectrum, and the received signal spectrum, and outputs an interference center frequency estimate and an estimated interference bandwidth; suppresses degradation due to noise emphasis by combining, for each frequency, spectral components within an interference band and spectral components within a band not containing interference, according to the ratio between the interference power included in the null symbol spectrum and the residual noise power included in the received signal spectrum after interference removal, using the received signal spectrum, the data symbol power estimate, the null symbol spectrum, the interference center frequency estimate, and the estimated interference bandwidth. A storage medium that causes the interference removal device to perform the above.

6. A first step in which a data symbol extraction unit extracts a data symbol portion from a received signal in which null symbols have been inserted into data symbols, and outputs a data symbol signal; a second step in which a null symbol extraction unit extracts a null symbol portion from the received signal, and outputs a null symbol signal; a third step in which a null symbol power calculation unit calculates a null symbol power estimate indicating the power of the null symbol signal; a fourth step in which a data symbol power calculation unit calculates a data symbol power estimate indicating the power of the data symbol signal; a fifth step in which a null symbol spectrum calculation unit calculates a null symbol spectrum from the null symbol signal; a sixth step in which a received signal spectrum calculation unit calculates a received signal spectrum from the received signal; and a seventh step in which an interference center frequency estimation unit estimates a center frequency and bandwidth of an interference signal using the data symbol power estimate, the null symbol spectrum, and the received signal spectrum, and outputs an interference center frequency estimate and an estimated interference bandwidth. an eighth step in which the interference removal unit suppresses degradation due to noise emphasis by combining, for each frequency, spectral components within an interference band and spectral components within a band not containing interference, using the received signal spectrum, the data symbol power estimate, the null symbol spectrum, the interference center frequency estimate, and the estimated interference bandwidth, in accordance with a ratio between interference power contained in the null symbol spectrum and residual noise power contained in the received signal spectrum after interference removal.

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