JP4704229B2 - Receiver - Google Patents

Description

  The present invention relates to a receiving apparatus, and more particularly to a receiving apparatus that receives a multicarrier signal.

In a broadcasting system such as a television broadcasting system, an OFDM (Orthogonal Frequency Division Multiplexing) modulation method may be used. The OFDM modulation scheme is one of multicarrier modulation schemes, and data to be transmitted is assigned to each of a plurality of mutually orthogonal subcarriers. In such an OFDM modulation scheme, a known pilot signal may be arranged on at least one of a plurality of subcarriers. In the receiving apparatus, the transmission path characteristic is estimated using the pilot signal, and equalization in the frequency domain is executed based on the estimated transmission path characteristic (see, for example, Patent Document 1).
JP-A-11-163822

  An error in equalization in the frequency domain becomes large, for example, in the following cases, and the reception characteristics of the reception apparatus deteriorate. The first is a case where interpolation is performed in order to derive a channel characteristic corresponding to another subcarrier from a channel characteristic corresponding to a pilot signal. As the interpolation, FFT (Fast Fourier Transform) is performed. ) (Hereinafter, such interpolation is referred to as “FFT interpolation processing”). That is, after inserting a value of “0” into a subcarrier that does not correspond to the pilot signal, IFFT is performed on the transmission path characteristic in which the value of “0” is inserted. As a result, the time domain transmission path characteristics are derived, and further, by extracting a part of the time domain transmission path characteristics and performing FFT, the frequency domain transmission path characteristics are derived. At this time, if a rectangular window filter is used when extracting a part of the time domain transmission line characteristics, a high-frequency component is generated and an error becomes large.

  The second case is a case where there is a carrier interference wave for the subcarrier in which the pilot signal is arranged. Here, the carrier interference wave is an interference wave having a bandwidth narrower than the bandwidth of the subcarrier. Since such interference waves exist continuously in time, even if processing for extracting a part of the transmission path characteristics in the time domain is executed, the influence of the interference waves remains. In particular, if the intensity of the interference wave is large, the error included in the weighting coefficient when executing the equalization process also increases. Furthermore, the third is a case where a deep notch exists in the band of the multicarrier signal. Since the signal strength is small in the subcarrier having a deep notch, the receiving apparatus increases the amplification factor. However, since the signal strength is small in the subcarrier having the notch, the accuracy of the signal component corresponding to the subcarrier is also lowered. When amplification is performed on such a signal component with a large amplification factor, the influence of an error included in the signal component increases, and reception characteristics deteriorate.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a receiving apparatus that reduces errors in equalization in the frequency domain.

In order to solve the above-described problems, a receiving apparatus according to an aspect of the present invention converts a received multicarrier signal and a multicarrier signal in which a known signal is arranged in at least one carrier into a frequency domain signal. Based on a first conversion unit, a known signal arranged in at least one of the signals converted in the first conversion unit, an estimation unit that estimates transmission path characteristics for the carrier, and an estimation unit A limiting unit that limits the amplitude of the transmission path characteristic to a predetermined range; and a predetermined value is inserted into a carrier other than the carrier corresponding to the transmission path characteristic limited by the limiting unit, and then the transmission path characteristic and the predetermined value are A second conversion unit that converts the combination into a signal in the time domain, a removal unit that removes part of the signal converted by the second conversion unit, and a part that is removed by the removal unit A third converter for converting signals into a signal in the frequency region, based on the converted signal in the third conversion portion, comprising a processing unit for processing the converted signal in the first conversion unit, the. When the second conversion unit inserts a predetermined value into a carrier other than the carrier corresponding to the transmission path characteristic estimated by the estimation unit, the second conversion unit sets the number of carriers smaller than the number of carriers that should actually insert the predetermined value. By inserting the predetermined value, the number of transmission path characteristics and the predetermined value included in one combination is less than the number of carriers included in the multicarrier signal, and the third conversion unit The number of components included in the signal converted into the frequency domain may be equalized with the number of carriers included in the multicarrier signal by performing interpolation on the signal converted into.

  According to this aspect, since the amplitude of the estimated transmission path characteristic is limited to a predetermined range, even if a carrier interference wave is included in the frequency where the known signal is arranged, the influence of the interference wave And an error in equalization in the frequency domain can be reduced.

Another embodiment of the present invention is also a receiving device. This apparatus is a received multicarrier signal, and a first conversion unit that converts a multicarrier signal in which a known signal is arranged on at least one carrier into a frequency domain signal, and a signal converted by the first conversion unit Based on a known signal arranged in at least one of the carriers, an estimation unit for estimating the channel characteristics for the carrier, and a predetermined value for a carrier other than the carrier corresponding to the channel characteristics estimated by the estimation unit A second conversion unit that converts a combination of transmission path characteristics and a predetermined value into a signal in the time domain, and a portion of the signal converted in the second conversion unit after time has elapsed The removal is performed by a filter having a characteristic in which the pass characteristic gradually becomes zero with time and the pass characteristic gradually increases from zero over time. A signal converted in the first conversion unit based on the signal converted in the third conversion unit, a third conversion unit that converts the signal partially removed in the removal unit into a signal in the frequency domain A processing unit. When the second conversion unit inserts a predetermined value into a carrier other than the carrier corresponding to the transmission path characteristic estimated by the estimation unit, the second conversion unit sets the number of carriers smaller than the number of carriers that should actually insert the predetermined value. By inserting the predetermined value, the number of transmission path characteristics and the predetermined value included in one combination is less than the number of carriers included in the multicarrier signal, and the third conversion unit The number of components included in the signal converted into the frequency domain may be equalized with the number of carriers included in the multicarrier signal by performing interpolation on the signal converted into.

  According to this aspect, since a filter whose pass characteristics gradually change with the passage of time is used, generation of high frequency components can be reduced, and errors in equalization in the frequency domain can be reduced.

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

  According to the present invention, errors in equalization in the frequency domain can be reduced.

  Before describing the present invention in detail, an outline will be described. An embodiment of the present invention relates to a receiving apparatus that receives a multicarrier signal in which a pilot signal is included in at least one of a plurality of subcarriers. The receiving apparatus estimates transmission path characteristics for a plurality of subcarriers by estimating transmission path characteristics corresponding to the pilot signal and performing FFT interpolation processing. As described above, a high frequency component can be generated by using a rectangular window in the FFT interpolation process. In addition, when the carrier wave interference wave is included in the subcarrier in which the pilot signal is arranged, the error included in the weighting coefficient increases. Further, when a notch is generated in the band of the multicarrier signal due to the presence of the delayed wave in the wireless transmission path, the receiving apparatus increases the amplification factor for the signal in the subcarrier corresponding to the notch. As a result, the influence of errors in the signal is also amplified. The receiving apparatus according to the embodiment of the present invention executes the following processing in order to cope with these.

  The receiving apparatus according to the present embodiment executes the following processing in order to reduce the influence of the carrier interference wave. That is, when the channel characteristics for the pilot signal are estimated, if the magnitude of the amplitude in the corresponding subcarrier is larger than the threshold value, the receiving apparatus limits the amplitude to a constant value. Further, in order to reduce the influence of high-frequency components that can be generated by the rectangular window in the FFT interpolation process, the receiving apparatus uses a window having a cosine roll-off characteristic instead of the rectangular window. Furthermore, in order to reduce the amplification of the influence of the error due to the notch, the receiving device limits the amplitude of the weighting factor to a predetermined value. Further, the receiving apparatus limits the amplitude in the demodulated result to a predetermined value.

  FIG. 1 shows a configuration of a receiving apparatus 100 according to an embodiment of the present invention. The receiving apparatus 100 includes an antenna 10, an RF unit 12, an orthogonal detection unit 14, an AD conversion unit 16, an FFT unit 18, a demodulation unit 20, a weighting factor derivation unit 22, and a control unit 24.

  The antenna 10 receives a multicarrier signal transmitted by a transmission device (not shown). FIG. 2 shows a configuration of a signal received by the antenna 10. The horizontal axis in the figure corresponds to frequency, and the vertical axis in the figure corresponds to time. That is, a plurality of circles arranged in the direction of the horizontal axis correspond to a plurality of subcarriers, and each of the subcarriers is “subcarrier # 1”, “subcarrier # 2”, “subcarrier # 3”. Indicated by etc. Also, black circles correspond to pilot signals, and white circles correspond to data signals. On the other hand, a plurality of circles arranged in the direction of the vertical axis correspond to a plurality of symbols, and each of the symbols is indicated by “symbol # 1”, “symbol # 2”, “symbol # 3”, or the like. A single symbol includes a plurality of subcarriers. Also, in consecutive symbols, pilot signals are arranged on different subcarriers. Returning to FIG.

  The RF unit 12 converts the frequency of the multicarrier signal received by the antenna 10. That is, since the received multicarrier signal has a radio frequency, the RF unit 12 converts the radio frequency multicarrier signal into an intermediate frequency multicarrier signal. Therefore, the RF unit 12 includes an amplifier, an oscillator, a mixer, a filter, and the like. However, these may be configured by a known technique, and thus description thereof is omitted here.

  The quadrature detection unit 14 performs quadrature detection on the intermediate-frequency multicarrier signal to generate a baseband multicarrier signal. Note that the baseband signal generally has an in-phase component and a quadrature component, and therefore should be indicated by two signal lines. Shown by signal line. The quadrature detection unit 14 includes an oscillator, a mixer, a filter, and the like. However, like the RF unit 12, these may be configured by a known technique, and thus description thereof is omitted here. The AD conversion unit 16 performs analog-digital conversion on the baseband multicarrier signal converted by the quadrature detection unit 14 and outputs a digital signal.

  The FFT unit 18 generates a multi-carrier signal in the frequency domain by performing FFT on the digital signal converted by the AD conversion unit 16. That is, the FFT unit 18 converts a multicarrier signal that is a received multicarrier signal and in which a pilot signal is arranged on at least one carrier, into a frequency domain signal. The weighting factor deriving unit 22 estimates transmission path characteristics for each subcarrier with respect to the signal converted into the frequency domain by FFT. Further, the weight coefficient deriving unit 22 derives a weight coefficient for each subcarrier from the estimated transmission path characteristics. The details of the processing in the weighting factor deriving unit 22 will be described later, but the above-described FFT interpolation processing is used.

  The demodulator 20 demodulates the signal converted to the frequency domain based on the weighting factor derived by the weighting factor deriving unit 22. That is, the demodulating unit 20 processes the signal converted in the FFT unit 18 based on the signal derived by the weighting factor deriving unit 22. Here, details of the processing in the demodulator 20 will also be described later. The control unit 24 controls the operation timing of the receiving device 100.

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

  FIGS. 3A to 3D show an outline of errors that can occur in the weighting factor deriving unit 22. FIG. 3A shows transmission path characteristics for a multicarrier signal in the frequency domain and transmission path characteristics in units of subcarriers. Here, as described above, the black circle corresponds to the pilot signal. That is, the transmission line characteristic for the black circle is derived by the process in the initial stage among the processes in the weighting factor deriving unit 22. In addition, an interference wave 200 is included in a subcarrier corresponding to one pilot signal. Note that the white circles in the drawing are shown for convenience and are not derived in the initial stage processing.

  FIG. 3B shows the result of executing IFFT on FIG. 3A, that is, the result of converting FIG. 3A to the time domain. Here, before executing IFFT, the weighting factor deriving unit 22 inserts “zero” into the subcarrier corresponding to the white circle in FIG. 3A, that is, the subcarrier on which the data signal is arranged. To do. As a result, in FIG. 3B, the preceding wave 202 and the delayed wave 204 appear, but they appear three periods. Further, the result of converting the jamming wave 200 into the time domain corresponds to the jamming wave 206.

  FIG. 3C corresponds to the result of extracting a part of the period in FIG. As shown in the drawing, a portion of one period or less is extracted from the transmission path characteristics in the time domain so that a set of preceding wave 202 and delayed wave 204 are included. At that time, a front part and a rear part are extracted. In addition, it is assumed that the aforementioned rectangular window is used when extracting. FIG. 3D corresponds to the result of converting FIG. 3C into the frequency domain. That is, as in FIG. 3A, this corresponds to the transmission path characteristic for the multicarrier signal in the frequency domain. However, in FIG. 3 (d), unlike FIG. 3 (a), transmission path characteristics for all subcarriers are derived. Further, since a rectangular window is used in FIG. 3C, a high frequency component is generated in FIG.

  FIG. 4 shows the configuration of the weighting factor deriving unit 22. The weighting factor deriving unit 22 includes a pilot extracting unit 30, a pilot estimating unit 32, a transmission path limiting unit 34, an inserting unit 36, an IFFT unit 38, a removing unit 40, an FFT unit 42, an interpolating unit 44, a calculating unit 46, and a weighting factor limiting. Unit 48 and amplitude calculation unit 50.

  The pilot extraction unit 30 extracts a pilot signal from the multicarrier signal converted into the frequency domain by the FFT unit 18 of FIG. That is, in FIG. 2, “subcarrier # 1”, “subcarrier # 13”, etc. of “symbol # 1” are extracted, and “subcarrier # 4”, etc. of “symbol # 2” are extracted.

  The pilot estimation unit 32 estimates transmission path characteristics for the pilot signal extracted by the pilot extraction unit 30. Since the pilot signal is a known signal, the pilot estimation unit 32 stores the value of the pilot signal in advance. In addition, the pilot estimation unit 32 estimates transmission path characteristics for the pilot signal by calculating the correlation between the pilot signal extracted by the pilot extraction unit 30 and the stored pilot signal. As a result, transmission path characteristics for “subcarrier # 1”, “subcarrier # 13”, etc., among “symbol # 1” in FIG. 2 are estimated.

  The transmission path limiting unit 34 limits the amplitude of the transmission path characteristics estimated by the pilot estimation unit 32 to a predetermined range. That is, the transmission path limiting unit 34 limits the amplitude, and converts the amplitude of the transmission path characteristic to a value having the limit when the amplitude of the transmission path characteristic is larger than the limitation. . Here, the limit value of the magnitude of the amplitude is calculated by an amplitude calculation unit 50 described later. Note that the transmission path limiting unit 34 may limit the amplitude of the transmission path characteristics so as to preserve the phase of the transmission path characteristics. For example, when the magnitude of the amplitude of the in-phase component of the transmission path characteristic is halved, the transmission path limiting unit 34 performs the orthogonal component of the transmission path characteristic regardless of the magnitude of the amplitude of the orthogonal component of the transmission path characteristic. The magnitude of the amplitude may also be halved.

  The insertion unit 36 inserts a value of “0” into subcarriers other than the subcarriers corresponding to the transmission path characteristics restricted by the transmission path restriction unit 34, that is, pilot signals are not arranged, and subcarriers are arranged with data signals. To do. Note that the value inserted by the insertion unit 36 does not have to be limited to “0”, and may be any value that has a small influence on the overall transmission path characteristics. Here, when inserting the value “0”, the insertion unit 36 inserts the value “0” into a smaller number of subcarriers than the number of subcarriers into which the value “0” is actually to be inserted. . For example, in the case of “symbol # 5” in FIG. 2, since the pilot signal is inserted in “subcarrier # 1”, “subcarrier # 13”, and the like, Accept the transmission path characteristics for the carrier. In addition, in “symbol # 2” to “symbol # 4”, the insertion unit 36 transmits to “subcarrier # 4”, “subcarrier # 7”, “subcarrier # 10”, “subcarrier # 16”, and the like. The road characteristics are already accepted. That is, the insertion unit 36 transmits the channel characteristics for the pilot signal at the symbol to be processed, for example, “symbol # 5”, and the pilot at the symbol before processing, for example, “symbol # 2” to “symbol # 4”. It accepts transmission path characteristics for signals. Therefore, a value of “0” should be inserted in subcarriers other than the above, for example, “subcarrier # 2”, “subcarrier # 3”, “subcarrier # 5”, “subcarrier # 6”, and the like. is there. That is, the process of inserting two consecutive “0” values, skipping one and inserting two consecutive “0” values should be repeated. However, the insertion unit 36 inserts one “0” value instead of two consecutive “0” values. As a result, the number of transmission path characteristics into which the number of values “0” is inserted is smaller than the number of subcarrier carriers included in the multicarrier signal.

  The IFFT unit 38 converts the combination into a time domain signal by performing IFFT on the combination input from the insertion unit 36 and the combination of the transmission path characteristic and the value “0”. . Because of the processing in the insertion unit 36, the number of points when the IFFT unit 38 executes IFFT is smaller than the number of points when the FFT unit 18 executes FFT.

  The removing unit 40 removes a part of the signal converted by the IFFT unit 38. Here, as described in FIG. 3C, the front part and the rear part are extracted from the transmission path characteristics in the time domain. However, the removal unit 40 does not use a square window at the time of removal, but uses a window having a cosine roll-off characteristic. That is, the removal unit 40 uses a filter having a characteristic that the pass characteristic gradually becomes zero with the passage of time and the pass characteristic gradually increases from zero with the further passage of time. Therefore, the removal unit 40 may use a Hanning window or a Hamming window. The removal unit 40 performs the removal using a rectangular window, and then smoothes the signal subjected to the removal using a low-pass filter such as an FIR (Finite Impulse Response) filter or an IIR (Infinite Impulse Response) filter. Also good.

  The amplitude calculation unit 50 calculates the limit value of the amplitude in the transmission line limiting unit 34 based on the signal from which a part has been removed by the removal unit 40. As will be described in detail later, the signal from which a part is removed by the removing unit 40 generally includes a preceding wave and a delayed wave. The amplitude calculation unit 50 adaptively calculates the amplitude limit value based on the signal strength of the preceding wave and the signal strength of the delayed wave. That is, the amplitude calculation unit 50 adds the signal strength of the preceding wave and the signal strength of the delayed wave, and derives a limit value according to the addition result. The width of the transmission line characteristic value is defined by deriving the ratio of the signal intensity of the preceding wave and the delayed wave (hereinafter referred to as “DU ratio”) and the signal intensity of the preceding wave. The calculation unit 50 may consider the width of the transmission line characteristic value when calculating the limit value. The amplitude calculation unit 50 may consider the maximum value and the minimum value of the slope of the transmission path characteristic value. In addition, the amplitude calculation unit 50 may perform smoothing on the transmission path estimation value of the interference wave, the periphery thereof, or the entire band, and derive the limit value based on the smoothing result. Here, the smoothing is realized by an average, a moving average, an FIR filter, and an IIR filter.

  The FFT unit 42 converts the signal into a frequency domain signal by performing FFT on the signal partially removed by the removing unit 40. Here, the FFT unit 42 performs the FFT after combining the front part and the rear part of the time-domain transmission path characteristics. The interpolation unit 44 performs interpolation on the frequency domain signal converted by the FFT unit 42 to thereby determine the number of components included in the frequency domain signal and the number of subcarriers included in the multicarrier signal. Are equal. That is, since the number of signals included in the frequency domain signal is equal to the number of components included in the combination from the insertion unit 36, the number is smaller than the number of subcarriers included in the multicarrier signal. The interpolation unit 44 performs interpolation using a higher-order function or linear interpolation, and any known technique may be used for these, and thus description thereof is omitted here.

  The calculation unit 46 derives a weighting factor for each of a plurality of subcarriers included in the multicarrier signal based on the transmission path characteristics derived by the interpolation unit 44. The calculation unit 46 derives a weighting coefficient by calculating the reciprocal of the transmission path characteristic for each subcarrier. The weighting factor limiting unit 48 limits the amplitude of the weighting factor derived by the calculation unit 46 to a predetermined range. The limit value by the weight coefficient limiter 48 is determined as follows.

In the following, in order to simplify the explanation, attention is paid to one subcarrier of the multicarrier signal. The minimum reception strength Pi assumed per one subcarrier is 1/5617 of the minimum reception strength Pmin assumed per all subcarriers. Here, the number of subcarriers included in the multicarrier signal is assumed to be 5617. Moreover, 1/5617 is “−37.5 dB”. From these, Pi is shown as follows.
Pi [dBm] = Pmin-37.5 (1)
If the assumed DU ratio is xmin, the strength PNi at the deepest part of the notch is expressed as follows.
PNi [dBm] = Pi-20log ₁₀ (1-xmin) (2)
Here, when the PNi approaches the thermal noise level of the receiving apparatus 100, the error of the weighting coefficient increases. The thermal noise Ni per subcarrier is expressed as follows.
Ni [dBm] = ₁₀ log ₁₀ kTBF + 30 (3)
Here, “k” is the Boltzmann constant, “B” is the bandwidth, “T” is the temperature indicated in absolute temperature, and “F” is the noise figure. From the above, the limit value Wimax of the weighting coefficient is expressed as follows.
Wimax [dB] = PNi-Ni + α (4)
Here, “α” is a margin, which is a constant. Also, Pmin and xmin are defined in advance. Note that Pmin may be an actual measurement value, and xmin may be derived from a delay profile. In this case, Wimax is adaptively changed. In order to derive Pmin and xmin, a weight coefficient limit value calculation unit (not shown) may be added.

  FIGS. 5A to 5D show an overview of processing in the weighting factor deriving unit 22. Here, in order to describe the processing by the transmission path limiting unit 34 and the removal unit 40 in FIG. 4, the insertion unit 36 inserts a value of “0” into the subcarrier corresponding to the data signal. FIG. 5A shows transmission path characteristics for a multicarrier signal in the frequency domain and transmission path characteristics in units of subcarriers. Here, as in FIG. 3A, black circles correspond to pilot signals. That is, the transmission line characteristic for the black circle is derived by the process in the initial stage among the processes in the weighting factor deriving unit 22. Further, the transmission path limiting unit 34 limits the strength against the interference wave 200.

  FIG. 5B shows the result of IFFT performed on FIG. 5A, that is, the result of converting FIG. 5A into the time domain, as in FIG. 3B. Here, due to the restriction by the transmission line restriction unit 34, the intensity of the interference wave 206 is reduced. FIG. 5C corresponds to the result of extracting a part of the period shown in FIG. 5B, as in FIG. However, in FIG. 5C, a window having a cosine roll-off characteristic is used in the removing unit 40. FIG. 5D corresponds to the result of converting FIG. 5C into the frequency domain, as in FIG. 3D. However, in FIG. 5 (d), unlike the case of FIG. 3 (d), since a window having a cosine roll-off characteristic is used, the generation of high-frequency components is reduced.

  Here, the cut-out width of the signal is assumed to be one cycle, but it is not limited to this. That is, it may be a period shorter than one cycle depending on the card interval length. Further, only the peripheral portion of the preceding wave 202 and the delayed wave 204 may be cut out. In this case, the cutout position and cutout width are adjusted according to the delay time of the delayed wave 204. Further, the removal unit 40 may set “0” for a portion having a low intensity after cutting out one period. In that case, the influence of noise can be reduced.

  FIGS. 6A to 6D show another outline of processing in the weighting factor deriving unit 22. Here, in particular, the process of inserting the value “0” in the insertion unit 36 will be described. FIG. 6A shows transmission path characteristics for multicarrier signals in the frequency domain and transmission path characteristics in units of subcarriers. Here, as in FIG. 5A, black circles correspond to pilot signals. On the other hand, a white circle corresponds to a subcarrier into which a value “0” is to be inserted by the insertion unit 36. In FIG. 5 (a), a value of “0” is inserted for two subcarriers sandwiched between two pilot signals, whereas in FIG. 6 (a), sandwiched between two pilot signals. A value of “0” is inserted for one subcarrier. As a result, the number of components included in the multicarrier signal is reduced.

  FIG. 6B shows the result of IFFT performed on FIG. 6A, that is, the result of converting FIG. 5A into the time domain, as in FIG. 5B. Since the number of subcarriers in which the value of “0” is to be inserted is reduced in the insertion unit 36, the number of combinations of the preceding wave 202 and the delayed wave 204 is also reduced. That is, in FIG. 5B, there are three periods, whereas in FIG. 6B, there are two periods. FIG. 6C corresponds to the result of extracting a part of the period of FIG. 6B by the window of the cosine roll-off characteristic as in FIG. 5C.

  FIG. 6D corresponds to the result of converting FIG. 6C into the frequency domain, as in FIG. 5D. The FFT unit 42 in FIG. 4 derives transmission path characteristics corresponding to white circles and black circles. However, the original transmission path characteristics to be derived should correspond to black circles and x marks. Therefore, the interpolation unit 44 derives a transmission path characteristic corresponding to the x mark by interpolation of a high-order function while using the transmission path characteristics corresponding to the white circle and the black circle.

  FIG. 7 shows the configuration of the demodulator 20. The demodulator 20 includes an equalizer 60 and an amplitude limiter 62. The equalization unit 60 demodulates the frequency domain signal converted by the FFT unit 18 of FIG. 1 based on the weighting factor derived by the weighting factor deriving unit 22 of FIG. Here, since the weighting factor and the frequency domain signal each include components corresponding to a plurality of subcarriers, the equalization unit 60 associates the weighting factor with the frequency domain signal for each subcarrier. The above processing corresponds to equalization in the frequency domain. The amplitude limiting unit 62 limits the amplitude of the signal demodulated by the equalizing unit 60 to a predetermined range. Since the limitation by the amplitude limiting unit 62 may be performed in the same manner as the limitation by the transmission path limiting unit 34 in FIG. 4, description thereof is omitted here.

  The operation of the receiving apparatus 100 having the above configuration will be described. The antenna 10 receives a multicarrier signal, and the RF unit 12, the quadrature detection unit 14, and the AD conversion unit 16 convert the received multicarrier signal into a baseband digital signal. The FFT unit 18 derives a multicarrier signal in units of subcarriers by performing FFT on the baseband digital signal. The pilot estimation unit 32 estimates transmission path characteristics for pilot signals among subcarrier-based multicarrier signals. The transmission path limiting unit 34 limits the estimated amplitude of the transmission path characteristic to a predetermined value when the estimated amplitude of the transmission path characteristic is larger than a predetermined value.

  Insertion unit 36 inserts a value of “0” into a portion other than the pilot signal in the subcarrier-based multicarrier signal, and generates a combination of the channel characteristic and the value of “0”. The IFFT unit 38 converts the combination into a time domain signal by performing IFFT on the combination. The removal unit 40 extracts a part of the signal in the time domain by using a window having a cosine roll-off characteristic. The FFT unit 42 performs IFFT on a partially extracted signal to convert the signal into the frequency domain, and the interpolation unit 44 performs interpolation on the frequency domain signal to perform the interpolation. The number of signal components is made equal to the number of subcarriers. As a result of the above processing, transmission path characteristics corresponding to each of the subcarriers are derived.

  The calculator 46 derives a weighting factor corresponding to each subcarrier by calculating the reciprocal of the transmission path characteristic. The weighting factor limiting unit 48 limits the amplitude of the weighting factor to a predetermined value when the amplitude of the weighting factor is larger than a predetermined value. The equalization unit 60 demodulates the subcarrier-based multicarrier signal derived by the FFT unit 18 using the weighting coefficient. The amplitude limiting unit 62 limits the amplitude of the demodulated signal to a predetermined value when the amplitude of the demodulated signal is larger than a predetermined value.

  According to the embodiment of the present invention, since the amplitude of the channel characteristic estimated for the pilot signal is limited to a predetermined range, the frequency where the pilot signal is arranged includes a carrier interference wave. Even if it exists, the influence by the said interference wave can be reduced. In addition, since the influence of the interference wave is reduced, an error in equalization in the frequency domain can be reduced. Also, since errors in equalization in the frequency domain can be reduced, reception characteristics can be improved. In addition, when extracting a part of the signal in the time domain, the use of a filter whose pass characteristics gradually change with time can reduce the generation of high frequency components. In addition, since the generation of high frequency components is reduced, the accuracy of the weighting factor can be improved. In addition, since the accuracy of the weighting factor is improved, an error in equalization in the frequency domain can be reduced.

  Further, since the amplitude of the demodulated signal is limited to a predetermined range, it is possible to suppress an increase in the amplitude of the signal amplified with a large amplification factor. Further, since the amplitude of the signal amplified with a large amplification factor is suppressed, an error in equalization in the frequency domain can be reduced. Further, since the amplitude of the weight coefficient is limited to a predetermined range, signal amplification due to a large amplification factor can be prevented. Further, since amplification of signals with a large amplification factor is prevented, errors in equalization in the frequency domain can be reduced.

  In addition, since the value of “0” is inserted into a smaller number of subcarriers than the number of subcarriers into which the value of “0” should actually be inserted, the number of components to be processed in the subsequent IFFT and FFT is reduced. it can. Further, since the number of components to be processed is reduced, the amount of processing can be reduced. Further, by performing interpolation after the FFT, the channel characteristics for each of the subcarriers included in the multicarrier signal are derived, so that demodulation can be performed.

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

  In the embodiment of the present invention, the transmission path limiting unit 34 limits the amplitude, the removal unit 40 extracts the cosine roll-off characteristic through the window, the weighting factor limiting unit 48 limits the amplitude, and the amplitude limiting unit 62 limits the amplitude. Of these, only the amplitude limitation by the transmission path limiting unit 34 may be performed. According to this modification, it is possible to reduce the influence of at least carrier interference waves while suppressing an increase in processing amount. That is, it is only necessary to reduce errors that affect reception characteristics.

  In the embodiment of the present invention, the transmission path limiting unit 34 limits the amplitude, the removal unit 40 extracts the cosine roll-off characteristic through the window, the weighting factor limiting unit 48 limits the amplitude, and the amplitude limiting unit 62 limits the amplitude. Of these, only extraction by the window of the cosine roll-off characteristic in the removing unit 40 may be performed. According to this modification, generation of high frequency components can be suppressed while suppressing an increase in processing amount. That is, it is only necessary to reduce errors that affect reception characteristics.

  In the embodiment of the present invention, the transmission path limiting unit 34 limits the amplitude, the removal unit 40 extracts the cosine roll-off characteristic through the window, the weighting factor limiting unit 48 limits the amplitude, and the amplitude limiting unit 62 limits the amplitude. Of these, only the amplitude limitation by the amplitude limiting unit 62 may be executed. According to this modification, it is possible to reduce the influence of the presence of deep notches while suppressing an increase in the processing amount. That is, it is only necessary to reduce errors that affect reception characteristics.

  In the embodiment of the present invention, the weight coefficient limiting unit 48 determines a limit value in advance. However, the present invention is not limited to this. For example, the weighting factor limiting unit 48 adaptively adjusts the limiting value based on the spectrum after equalization by the demodulating unit 20, the MER in units of subcarriers, or the BER in units of subcarriers. Also good. In order to execute the above processing, a weighting factor calculation unit may be added. According to this modification, the limit value can be accurately derived.

The invention according to the present embodiment may be specified by the following items.
(Item 1)
A conversion unit that converts a multicarrier signal that is a received multicarrier signal and a known signal is arranged in at least one carrier into a frequency domain signal;
Based on a known signal arranged in at least one of the signals converted in the conversion unit, an estimation unit that estimates transmission path characteristics for the carrier;
A derivation unit for deriving a weighting factor for each of a plurality of carriers included in the multicarrier signal based on the transmission path characteristics estimated by the estimation unit;
Based on the weighting factor derived in the derivation unit, a demodulation unit that demodulates the signal converted in the conversion unit,
A limiting unit that limits the amplitude of the signal demodulated in the demodulation unit to a predetermined range;
A receiving apparatus comprising:

(Item 2)
The receiving device according to item 1, wherein the derivation unit limits the amplitude of the derived weighting factor to a predetermined range.

It is a figure which shows the structure of the receiver which concerns on the Example of this invention. It is a figure which shows the structure of the signal received in the antenna of FIG. 3A to 3D are diagrams showing an outline of errors that can occur in the weighting factor deriving unit of FIG. It is a figure which shows the structure of the weighting factor derivation | leading-out part of FIG. FIGS. 5A to 5D are diagrams showing an outline of processing in the weighting factor deriving unit in FIG. FIGS. 6A to 6D are diagrams showing another outline of processing in the weighting factor deriving unit in FIG. It is a figure which shows the structure of the demodulation part of FIG.

Explanation of symbols

  10 antennas, 12 RF units, 14 quadrature detection units, 16 AD conversion units, 18 FFT units, 20 demodulation units, 22 weight coefficient deriving units, 24 control units, 100 receiving apparatuses.

Claims (2)

A first conversion unit that converts a received multicarrier signal and a multicarrier signal in which a known signal is arranged in at least one carrier into a frequency domain signal;
An estimation unit that estimates transmission path characteristics for the carrier based on a known signal arranged in at least one of the signals converted in the first conversion unit;
A limiting unit that limits the amplitude of the transmission path characteristic estimated in the estimation unit to a predetermined range;
A second conversion unit that converts a combination of the transmission path characteristic and the predetermined value into a signal in a time domain after inserting a predetermined value into a carrier other than the carrier corresponding to the transmission path characteristic limited in the limiting unit;
A removing unit for removing a part of the signal converted in the second converting unit;
A third conversion unit that converts the signal partially removed in the removal unit into a frequency domain signal;
A processing unit for processing the signal converted in the first conversion unit based on the signal converted in the third conversion unit ;
When the second conversion unit inserts a predetermined value into a carrier other than the carrier corresponding to the transmission path characteristic estimated by the estimation unit, the second conversion unit is smaller in number than the number of carriers that should actually insert the predetermined value. By inserting a predetermined value into the carrier, the number of transmission path characteristics and the predetermined value included in one combination is less than the number of carriers included in the multicarrier signal,
The third conversion unit performs interpolation on the signal converted into the frequency domain, thereby calculating the number of components included in the signal converted into the frequency domain and the number of carriers included in the multicarrier signal. A receiving device characterized by equalization . A first conversion unit that converts a received multicarrier signal and a multicarrier signal in which a known signal is arranged in at least one carrier into a frequency domain signal;
An estimation unit that estimates transmission path characteristics for the carrier based on a known signal arranged in at least one of the signals converted in the first conversion unit;
A second conversion unit that inserts a predetermined value into a carrier other than the carrier corresponding to the transmission path characteristic estimated by the estimation unit, and then converts a combination of the transmission path characteristic and the predetermined value into a signal in the time domain;
With respect to a part of the signal converted in the second conversion unit, the passage characteristic gradually becomes zero as time passes, and the passage characteristic gradually increases from zero as time passes further. A removal unit for performing removal by a filter;
A third conversion unit that converts the signal partially removed in the removal unit into a frequency domain signal;
A processing unit for processing the signal converted in the first conversion unit based on the signal converted in the third conversion unit ;
When the second conversion unit inserts a predetermined value into a carrier other than the carrier corresponding to the transmission path characteristic estimated by the estimation unit, the second conversion unit is smaller in number than the number of carriers that should actually insert the predetermined value. By inserting a predetermined value into the carrier, the number of transmission path characteristics and the predetermined value included in one combination is less than the number of carriers included in the multicarrier signal,
The third conversion unit performs interpolation on the signal converted into the frequency domain, thereby calculating the number of components included in the signal converted into the frequency domain and the number of carriers included in the multicarrier signal. The receiving device according to claim 1, wherein the receiving devices are equal .

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