JP5896393B2 - Receiving apparatus and receiving method - Google Patents

Description

  The present invention relates to an orthogonal frequency division multiplexing (hereinafter abbreviated as OFDM) signal receiving apparatus and receiving method.

  For example, in a terrestrial digital broadcasting signal transmission system such as ISDB-T and DVB-T, a known pilot carrier is assigned to a transmission signal on the transmission side so that the characteristics of the transmission path can be easily estimated on the reception side. ing. In such a signal transmission system, it is important to correctly estimate the transmission path from the pilot carrier because the reception performance is greatly affected by the estimation accuracy of the transmission path.

  Also, various methods have been proposed for techniques using a pilot carrier. For example, in a signal transmission system in which pilot carriers are allocated at regular intervals in the time direction and frequency direction of a transmission signal, a reception technique is known in which a signal is demodulated after obtaining a transmission path estimation value for the pilot carrier.

Furthermore, when estimating a transmission path using an interpolation filter, it is known that suppressing the noise component passing through the interpolation filter improves the estimation accuracy of the transmission path and improves the reception performance. . For example, Patent Document 1 discloses a technique for determining a pass band of an interpolation filter based on an arrival wave having the longest delay time among arrival waves of a transmission signal generated on a transmission path.
In the apparatus described in Patent Document 1, since the high frequency component after the maximum delay time included in the received signal is suppressed, the noise component remaining in the transmission path estimation value obtained as an interpolation result can be reduced.

  Patent Document 2 discloses a technique for performing interpolation processing by multi-rate filter processing that reconstructs only necessary signal components using filters that divide input signals into a plurality of subbands.

  Further, Patent Document 3 discloses a technique for performing frequency direction interpolation with a plurality of different bandpass filters for each incoming wave estimated by a delay profile. In Patent Document 3, the output signal of the time direction interpolation filter is filtered for each incoming wave, and a desired transmission path estimation result can be obtained by adding (synthesizing) the filter outputs. For this reason, the pass band of the frequency direction interpolation filter can be controlled, and the noise component can be suppressed.

Japanese Patent Laid-Open No. 10-75226 JP 2000-286821 A JP 2010-246024 A

  In the technique of Patent Document 1, the interpolation filter is configured by a low-pass filter, and high-frequency components after the maximum delay time are suppressed, but noise components other than the desired signal component are included in the pass-band. It is. Therefore, there is a problem that the noise suppression effect is insufficient.

  Patent Document 2 suppresses the frequency response estimated value after the maximum delay time, as in Patent Document 1. Moreover, in order to implement | achieve multirate filter processing like patent document 2, it is necessary to comprise a some filter in multistage. Therefore, there is a problem that it is difficult to realize a configuration that can follow various actual radio wave environments because the circuit becomes large or the amount of calculation becomes enormous.

  Furthermore, the conventional technique disclosed in Patent Document 3 has a configuration in which each band-pass filter operates individually to synthesize their outputs. For this reason, depending on the delay profile of the transmission path and the frequency characteristics of each bandpass filter, there is a problem that more than necessary arrival wave components remain in the combined result of the filter outputs, and a correct transmission path estimation result cannot be obtained.

  For example, when an incoming wave component remains in a transition band between the pass band and the stop band of the bandpass filter, the filter gain for each incoming wave does not become a desired gain due to the residual component. For this reason, as a result, the transmission path estimation result has a different characteristic from the actual transmission path, and the quality of the demodulated signal deteriorates. Such a phenomenon in which an incoming wave component remains in the transition region of a bandpass filter is more likely to occur as the passbands of adjacent bandpass filters are closer.

If the transition region of the bandpass filter is made as steep as possible, the above reduction can be avoided to some extent. However, the number of taps of the filter is finite, and there is a limit even if the transition region is narrowed. Further, under a finite number of filter taps, the steepness of the frequency characteristics in the transition region causes tradeoffs such that the passband ripple increases and the attenuation in the stopband cannot be sufficiently secured.
As new problems arise in this way, they are not fundamental solutions.

  The present invention has been made to solve the above-described problems, and provides a receiving apparatus and a receiving method capable of accurately suppressing a noise component of a transmission line and improving reception performance with a simple configuration. With the goal.

  A receiving apparatus according to the present invention is a receiving apparatus for receiving an OFDM signal to which a known pilot carrier is allocated in the time direction and the frequency direction, and a Fourier transform unit that outputs the received signal by performing a discrete Fourier transform for each OFDM symbol And a pilot carrier extraction unit that extracts and outputs a signal corresponding to the pilot carrier from the output signal of the Fourier transform unit, and the transmission path characteristics for the pilot carrier estimated based on the output signal of the pilot carrier extraction unit in the time direction. A time-interpolation filter unit that outputs by inserting, a delay profile detection unit that detects and outputs a delay profile of the transmission path from the output signal of the time interpolation filter unit, and a transmission path based on the output signal of the delay profile detection unit When an incoming wave component is detected and a subband including the incoming wave component is determined In addition, when there is an overlapping part other than the stopband in the frequency characteristics between the filters that pass adjacent subbands, a passband determination unit that determines a subband including each of these subbands, and a passband determination unit A pass band for passing the determined sub-band, and a frequency interpolation filter unit for band-limiting the output signal of the time interpolation filter unit to interpolate the transmission line characteristics for the pilot carrier in the frequency direction, and a Fourier transform And an equalization unit that performs demodulation for each subcarrier by dividing the output signal of the unit by the output signal of the frequency interpolation filter unit.

  According to the present invention, there is an effect that the reception performance can be improved by accurately suppressing the noise component of the transmission path with a simple configuration.

It is a block diagram which shows the structure of the receiver which concerns on Embodiment 1 of this invention. It is a figure which shows the example of arrangement | positioning of a pilot carrier. 3 is a flowchart showing an operation of the receiving apparatus according to the first embodiment. 3 is a block diagram illustrating a configuration of a frequency interpolation filter unit in the first embodiment. FIG. It is a figure which shows a filter output spectrum. It is a figure which shows an example of a delay profile. 3 is a block diagram illustrating a configuration of a filter coefficient generation unit according to Embodiment 1. FIG. 3 is a block diagram showing a configuration of a passband determination unit in Embodiment 1. FIG. It is a figure which shows the detection result of a delay profile and an incoming wave component. It is a figure which shows the data obtained by the determination process of a pass band by a passband determination part (when an incoming wave component does not exist in a transition area). It is a figure which shows a delay profile in case an incoming wave component exists in the transition area between adjacent filters. It is a figure which shows the data obtained by the determination process (when an incoming wave component exists in a transition area) by the passband determination part. It is a block diagram which shows the structure of the frequency interpolation filter part in Embodiment 2 of this invention.

Hereinafter, in order to describe the present invention in more detail, modes for carrying out the present invention will be described with reference to the accompanying drawings.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a receiving apparatus according to Embodiment 1 of the present invention. The receiving apparatus illustrated in FIG. 1 is a receiving apparatus that receives an OFDM signal. Note that the transmission side performs primary modulation on transmission data with QAM (Quadrature Amplitude Modulation) or QPSK (Quadrature Phase Shift Keying) and assigns pilot carriers at regular intervals in the time and frequency directions. Send by transmission method.

  The Fourier transform unit 1 performs discrete Fourier transform on the received signal S1 converted into the baseband band for each OFDM symbol, and outputs the result. Each subcarrier component transmitted by the OFDM method is obtained as a frequency domain signal output from the Fourier transform unit 1.

  The pilot carrier extraction unit 2 extracts a signal corresponding to the pilot carrier from the output signal of the Fourier transform unit 1 and outputs it. For example, in terrestrial digital broadcasting such as ISDB-T and DVB-T, as shown in FIG. 2, there are known pilot carriers every 4 symbols in the time direction (symbol direction) and every 12 carriers in the frequency direction (carrier direction). Has been inserted. The estimation of transmission path characteristics is realized by interpolating the transmission path estimation result for the pilot carrier in the time direction and the frequency direction.

The time interpolation filter unit 3 interpolates in the time direction the transmission path characteristics for the pilot carrier estimated based on the output signal of the pilot carrier extraction unit 2.
For example, the time interpolation filter unit 3 divides a received signal (Fourier transform output value) corresponding to a pilot carrier by a known signal corresponding to the pilot carrier, and estimates a transmission path characteristic corresponding to the pilot carrier. Then, the channel characteristics corresponding to the pilot carrier are interpolated in the time direction for each same subcarrier frequency and output.

  The frequency interpolation filter unit 4 is set with a pass band through which the subband determined by the passband determination unit 6 is passed, and the output signal of the time interpolation filter unit 3 is band-limited to change the transmission path characteristics for the pilot carrier to the frequency. Interpolate in the direction. That is, the channel characteristics interpolated in the time direction by the time interpolation filter unit 3 are also interpolated in the frequency direction by the frequency interpolation filter unit 4, and the channel characteristic estimation results of all subcarriers are obtained. .

  The delay profile detection unit 5 detects the delay profile of the transmission path from the output signal of the time interpolation filter unit 3. For example, the inverse discrete Fourier transform is performed on the output signal of the time interpolation filter unit 3, and the square value of the amplitude of each complex signal obtained by this conversion is used as the delay profile.

The passband determination unit 6 detects an incoming wave component of the transmission path based on the output signal of the delay profile detection unit 5 and determines a subband that is a partial band including the incoming wave component.
For example, based on the delay profile, the arrival time and power value of a transmission signal (hereinafter also referred to as an incoming wave) that arrives by repeatedly reflecting or diffracting on the transmission path are detected, and the frequency band (sub- Band).
The pass band for allowing the passband determined by the passband determining unit 6 to pass is controlled to have a necessary and sufficient bandwidth for passing all the incoming wave components detected based on the delay profile. .
Therefore, the number of pass bands is not limited to one, and there may be two or more pass bands depending on the state of the transmission path. The passband determination unit 6 sets a frequency band including an incoming wave component as a subband, and sets a passband through which the subband passes through the frequency interpolation filter unit 4 using filter type control information and shift control information described later.

In addition, when there is an overlapping portion other than the stop band in the frequency characteristics between the filters that allow the adjacent subbands to pass through, the passband determination unit 6 determines again the subbands including these subbands.
Note that the overlapping part other than the stop band corresponds to any of an overlapping part of pass bands, an overlapping part of the pass band and the transition area, and an overlapping part of the transition areas in the frequency characteristic between the filters. When this overlap portion exists, the same incoming wave component may be separately passed through adjacent filters, and the filter gain may not be a desired gain. In this case, as a result, the transmission path estimation result has a characteristic different from that of the actual transmission path, and the quality of the demodulated signal is deteriorated.
Therefore, if there is an overlapping portion as described above, the passband determining unit 6 re-determines subbands each including adjacent subbands.

  The equalization unit 7 divides the output signal of the Fourier transform unit 1 by the output signal of the frequency interpolation filter unit 4 and performs demodulation for each subcarrier. As a result, a demodulated signal S2 for each subcarrier is obtained and output to the subsequent stage.

  The Fourier transform unit 1, pilot carrier extraction unit 2, time interpolation filter unit 3, frequency interpolation filter unit 4, delay profile detection unit 5, passband determination unit 6 and equalization unit 7 are realized as hardware circuits. Is possible. In addition, the above-described components 1 to 7 can be realized as specific means in which hardware and software cooperate by, for example, a microcomputer executing a program in which processing unique to the present invention is described. Can do.

Next, the operation will be described.
FIG. 3 is a flowchart showing an operation of the receiving apparatus according to Embodiment 1.
First, the Fourier transform unit 1 performs discrete Fourier transform on the received signal S1 for each OFDM symbol (step ST1).
Next, the pilot carrier extraction unit 2 extracts and outputs a signal corresponding to the pilot carrier included in the received signal from the output signal of the Fourier transform unit 1 (step ST2).
The time interpolation filter unit 3 estimates the channel characteristics for the pilot carrier based on the output signal of the pilot carrier extraction unit 3, and interpolates the estimated channel characteristics in the time direction for each subcarrier (step ST3).
Next, the delay profile detection unit 5 performs inverse discrete Fourier transform on the output signal of the time interpolation filter unit 3, and outputs the square value of the amplitude of the complex signal obtained by this conversion as a delay profile (step ST4). ).

The passband determination unit 6 determines subbands each including an incoming wave component of the transmission path detected based on the output signal of the delay profile detection unit 5, and sets the passband through which the determined subband is passed to the frequency interpolation filter unit Is set to 4 (step ST5).
In addition, when there exists an overlapping part other than a stop band in the frequency characteristic between the filters which each pass an adjacent subband, the passband determination part 6 determines again the subband containing each of these subbands.

The frequency interpolation filter unit 4 is set with a pass band through which the subband determined by the passband determination unit 6 is passed, and the output signal of the time interpolation filter unit 3 is band-limited to change the transmission path characteristics for the pilot carrier in the frequency direction. (Step ST6).
The channel characteristics interpolated in the time direction by the time interpolation filter unit 3 are also interpolated by the frequency interpolation filter unit 4 in the frequency direction, and the channel characteristic estimation results of all subcarriers are sent to the equalization unit 7. Is output.
After that, the equalizing unit 7 divides the output signal of the Fourier transform unit 1 by the output signal of the frequency interpolation filter unit 4 and demodulates each subcarrier, and outputs a demodulated signal S2 for each subcarrier (step ST7). ).

  Next, the configuration and detailed operation of the frequency interpolation filter unit 4 in the first embodiment will be described. FIG. 4 is a block diagram showing the configuration of the frequency interpolation filter unit in the first embodiment, and it is possible to realize three band-pass filters that allow a maximum of three subbands to pass through. As shown in FIG. 4, the frequency interpolation filter unit 4 in the first embodiment includes subband filter units 41 a to 41 c, filter coefficient generation units 42 a to 42 c, and an output addition unit 43.

  The subband filter unit 41a is a filter that sets a pass band based on the filter coefficient generated by the filter coefficient generation unit 42a and limits the band of the output signal of the time interpolation filter unit 3. Similarly, the passband is set in the subband filter unit 41b based on the filter coefficient generated by the filter coefficient generation unit 42b, and the subband filter unit 41c is passed based on the filter coefficient generated by the filter coefficient generation unit 42c. Bands are set, and each band-limits the output signal of the time interpolation filter unit 3. The subband filter units 41a to 41c are filters having different bandwidths.

The filter coefficient generation unit 42a receives the filter type control information a and the shift control information a from the passband determination unit 6 and determines the passband of the subband filter selected based on the filter type control information a as the shift control information. A filter coefficient shifted in frequency based on a is generated. This filter coefficient is, for example, a filter coefficient that constitutes a bandpass filter that is effective for the subband including the first incoming wave component with the shortest delay time in the delay profile.
Similarly, the filter coefficient generation unit 42b is a filter coefficient obtained by frequency-shifting the passband of the subband filter selected based on the filter type control information b input from the passband determination unit 6 based on the shift control information b. Is generated.
For example, this filter coefficient is a filter coefficient constituting a bandpass filter effective for a subband including the second incoming wave component having the next shortest delay time.
The filter coefficient generation unit 42c generates a filter coefficient obtained by frequency-shifting the passband of the subband filter selected based on the filter type control information c input from the passband determination unit 6 based on the shift control information c. .
For example, this filter coefficient is a filter coefficient constituting a bandpass filter effective for the subband of the incoming wave component having the third smallest delay time.

  FIG. 4 shows a configuration that can handle a maximum of three subbands. However, when one or two subbands are sufficient to pass all incoming wave components, the subband filter units 41a to 41a Filter coefficients are generated from 41c such that one or two subband filter units are enabled. The output signals of the subband filter units 41 a to 41 c are added by the output adding unit 43 and output to the equalizing unit 7.

Next, the pass band of the frequency interpolation filter unit 4 will be described.
The frequency interpolation filter unit 4 is a filter for performing an interpolation process in the frequency direction of subcarriers to obtain an estimated value of transmission path characteristics for all subcarriers.
Here, the frequency interpolation filter unit 4 used for estimating the transmission path characteristics needs to have a frequency band that allows all incoming wave components necessary for demodulation to pass therethrough.
At the same time, when the pass band of the filter includes a frequency band in which no incoming wave component exists, the noise component passes through the filter, so that the estimation accuracy of the transmission path characteristics is lowered and the reception performance is deteriorated. This means that it is desired to realize the frequency interpolation filter unit 4 having the minimum necessary pass band.

  For example, as shown in the delay profile of FIG. 5A, a transmission path through which two incoming wave components consisting of a main wave and a delayed wave are transmitted will be described as an example. Here, the horizontal axis represents the arrival time of the incoming wave component, and the vertical axis represents the power. When the pass band of the frequency interpolation filter is not controlled, as shown in FIG. 5B, the low pass filter includes all incoming wave components in the pass band. In this case, although the high frequency component is removed, many noise components uniformly distributed over the entire signal band such as thermal noise other than the incoming wave component pass through the filter.

On the other hand, if a filter that passes only the incoming wave component can be realized, the passage of the noise component can be significantly suppressed as shown in FIG.
In an actual transmission path, there may be a plurality of incoming wave components as shown in FIG. 6A, and a delay spread is caused by a plurality of incoming wave components as shown in FIG. 6B. In some cases. Furthermore, when a signal is received while the receiving apparatus is moving, the transmission path changes momentarily as the receiving apparatus moves, so the receiving apparatus adaptively follows such a change in the transmission path. There is a need.

The frequency interpolation filter unit 4 according to the first embodiment includes a plurality of filters (subband filter units) having different bandwidths, selects a filter from these filters according to an actual delay profile, and passes the filter. By shifting the frequency of the band, only the subband which is a partial band of the incoming wave component is passed.
On the other hand, in the conventional frequency interpolation filter disclosed in Patent Document 1, as shown in FIG. 5 (b), the low frequency band includes the component with the longest delay time among the incoming wave components. A pass filter is configured. For this reason, the longer the delay time of the incoming wave component is, the wider the pass band becomes, and the noise component in the pass band increases, so that sufficient reception performance cannot be obtained.

Further, Patent Document 2 realizes a desired frequency characteristic by reconstructing only necessary signal components by multi-rate filter processing. However, as the number of passbands through which signal components pass increases, the size of the receiving device increases. Increases and complicates signal processing.
In contrast, in the first embodiment, a filter corresponding to the bandwidth of the subband is selected from a plurality of filters (subband filter units) having different bandwidths, and the passband of the selected filter is frequency-shifted. Set the passband that allows only the incoming wave component to pass.
Therefore, it is possible to obtain a desired frequency characteristic with a much simpler configuration than that of Patent Document 2.

Next, the configuration and operation of the filter coefficient generation units 42a to 42c of the frequency interpolation filter unit 4 will be described with reference to FIG. As shown in FIG. 7, the filter coefficient generation units 42 a to 42 c are configured to include a filter coefficient selection unit 421 and a passband shift unit 422.
The filter coefficient selection unit 421 selects the filter coefficient of the subband filter unit selected based on the filter type control information from the subband filter units 41a to 41c which are low-pass filters having different bandwidths. That is, the filter type control information is information indicating which filter is selected from the subband filter units 41a to 41c having different bandwidths.
For example, in the filter coefficient selection unit 421 of the filter coefficient generation unit 42a, when the filter type control information a for selecting the subband filter unit 41a is input, the filter coefficient that defines the bandwidth of the subband filter unit 41a is selected. And output to the passband shift unit 422.

The passband shift unit 422 selects filter coefficients so that the passband of the subband filter unit selected based on the filter type control information is frequency-shifted based on the shift control information so that the frequency characteristic becomes a desired passband. The filter coefficient selected by the unit 421 is converted.
For example, in the shift control information, the center frequency of a desired subband filter unit in which the center frequency of the passband matches the center of the subband is set. The passband shift unit 422 includes the filter coefficient of the low-pass filter selected by the filter coefficient selection unit 421 and the center of the desired subband filter unit in which the passband of the low-pass filter is set as shift control information. Complex multiplication is performed with a coefficient that shifts the frequency by the frequency. Thereby, a filter coefficient for generating a frequency shift based on the shift control information is generated for the pass band of the subband filter unit selected based on the filter type control information. A subband filter unit having a desired pass band is configured based on the filter coefficient.

Next, the configuration and operation of the passband determination unit 6 will be described.
FIG. 8 is a block diagram showing a configuration of the passband determination unit in the first embodiment. As shown in FIG. 8, the passband determination unit 6 includes an incoming wave component detection unit 61, a subband provisional determination unit 62, a filter type control unit 63, and a shift control unit 64.

  The incoming wave component detector 61 detects the presence / absence of the incoming wave component and the arrival time difference based on the delay profile. The presence / absence of the incoming wave component is determined, for example, by comparing a power value of each component of the delay profile with a predetermined threshold (hereinafter also referred to as a power determination threshold) and determining a component larger than the threshold as the incoming wave component. The power determination threshold is determined based on, for example, the component having the maximum power value. In this case, the power determination threshold is changed each time the output signal of the delay profile detection unit 5, that is, the delay profile of the transmission path is updated. For this reason, it becomes possible to determine the presence or absence of an incoming wave component according to a change in the radio wave environment.

  The arrival time difference is expressed as an index of inverse discrete Fourier transform (hereinafter also referred to as IFFT) performed by the delay profile detection unit 5. For example, when a delay profile is detected by 64-point IFFT, an IFFT result is obtained for each index from 0 to 63. This difference in index is proportional to the difference in arrival time of incoming wave components.

  The subband temporary determination unit 62 determines a subband including the incoming wave component detected by the incoming wave component detection unit 61. Here, the subband determination process will be specifically described. FIG. 9A shows an example of a delay profile detected by the delay profile detector 5. Further, it is assumed that the frequency interpolation filter unit 4 can realize three band-pass filters that allow a maximum of three subbands to pass through. Accordingly, the incoming wave component detection unit 61 is also configured to detect a maximum of three subbands.

The incoming wave component detection unit 61 compares the delay profile detection result shown in FIG. 9A and the power determination threshold value, and outputs the presence / absence of the incoming wave component to the subband provisional determination unit 62 as binary information.
Based on the information input from the incoming wave component detection unit 61, the subband provisional decision unit 62, as shown in FIG. 9B, is a section T1 with IFFT indexes from 4 to 16, and sections from 40 to 43. It is determined that there are incoming wave components in the sections T3 from T2, 59 to 63, and three partial bands, that is, subband a, subband b, and subband c are determined and stored. For example, the subband names of subbands a to c as shown in FIG. 10A and the IFFT indexes of the passbands corresponding to these are stored.

The filter type control unit 63 generates filter type control information for selecting a filter having a bandwidth that can pass through the subband determined by the subband temporary determination unit 62.
In the first embodiment, the frequency interpolation filter unit 4 includes a plurality of low-pass filters (sub-band filter units 41a to 41c in FIG. 4) having different pass bandwidths, and these low-pass filters are sub-bands. It becomes a subband filter candidate for passing.
The filter type control unit 63 is set with table data in which identification information of all the low-pass filters included in the frequency interpolation filter unit 4 is associated with the pass bandwidth.
An example of this table data is shown in FIG. In FIG. 10B, the pass bandwidth is represented by an IFFT index width.

The generation of the filter type control information will be described in detail. The filter type control unit 63 refers to the table data, and the pass band is the highest among the subband filter candidates having a pass bandwidth equal to or larger than the subband bandwidth. A subband filter candidate having a narrow width is discriminated, and filter type control information for selecting the subband filter candidate is generated.
At this time, it is desirable that the center frequency of the passband of the subband filter matches the frequency of the center of the subband, but this is not restrictive.

The filter type control unit 63 selects a subband filter for each subband, but the same subband filter may be selected in different subbands.
For example, in the case of FIG. 9B, the first incoming wave component is included in the subband a in the section T1 in which the IFFT index is 4 to 16, and the IFFT index width of the subband a is 12. Therefore, with reference to the table data of FIG. 10B, the subband having the narrowest passband width among the subband filter candidates (subband filters C and D) having a pass bandwidth equal to or larger than the bandwidth of subband a. A subband filter C which is a filter candidate is selected.

  In addition, the incoming wave component that arrives next in FIG. 9B is included in the subband b of the section T2 in which the IFFT index is 40 to 43, and the IFFT index width of the subband b is 3. Therefore, referring to the table data of FIG. 10B, the subband filter candidate having the narrowest passband width from the subband filter candidates (subband filters A to D) having a passband width equal to or larger than the bandwidth of subband b. A subband filter A is selected.

  Similarly, the arriving wave component with the longest delay time in FIG. 9B is included in the subband c of the section T3 in which the IFFT index is 59 to 63, and the IFFT index width of the subband c is 4. Therefore, with reference to the table data of FIG. 10B, the subband filter candidate having the narrowest passband width from the subband filter candidates (subband filters A to D) having a passband width equal to or larger than the subband c bandwidth. A subband filter A is selected. These determination results are shown in FIG.

The shift control unit 64 generates shift control information that shifts the frequency of the passband of the subband filter selected based on the filter type control information in accordance with the subband.
Specifically, in order to change the sub-band filter, which is a low-pass filter, to a band-pass filter that passes the sub-band, the shift amount for frequency-shifting the pass band of the low-pass filter is determined, and the determination result Shift control information in which the center frequency when the frequency is shifted by the shift amount is generated for each subband and output. Note that the shift amount can be represented by an IFFT index.

  For example, since the IFFT index of the subband a in the section T1 is 4 to 16, the center IFFT index is 10. That is, if the passband of the subband filter C is frequency shifted by IFFT index 0 to 10, the center frequency of the passband of the subband filter C coincides with the center of the subband a. Therefore, the passband shift amount (IFFT index) is 10.

  Similarly, the subband b in the section T2 has an IFFT index of 40 to 43, and its center IFFT index is 41. That is, if the passband of the subband filter A is frequency shifted by IFFT index 0 to 41, the center frequency of the passband of the subband filter C coincides with the center of the subband b. Therefore, the passband shift amount (IFFT index) is 41.

  Since the IFFT index is 59 to 63 for the subband c in the section T3, the IFFT index at the center is 61. That is, if the passband of the subband filter A is frequency-shifted by IFFT index 0 to 61, the center frequency of the passband of the subband filter A coincides with the center of the subband c. Therefore, the passband shift amount (IFFT index) is 61. A summary of these determination results is shown in FIG.

  Further, the filter type control unit 63 determines the frequency distance between the passband width of the subband filter that passes the subband determined by the temporary subband determination unit 62 and the subband filter that passes the adjacent subband. Based on this, it is determined whether or not there is an overlapping portion other than the stop band in the frequency characteristics between these subband filters. When there is no overlapping portion, the filter type control unit 63 adopts the subband determined by the subband temporary determination unit 62 as it is, and when there is the overlapping portion, the subband including each adjacent subband. Is again determined, and filter type control information for selecting a low-pass filter having a bandwidth through which the subband can pass is generated.

  When the interval between adjacent subbands is narrow, as a result of selecting an optimum subband filter for passing each subband, an overlapping portion other than the stopband occurs in the frequency characteristics between the subband filters. In the example shown in FIG. 11, there is an overlapping portion of the passband and the transition band between the subband filter BF1 that passes the incoming wave 1 and the subband filter BF2 that passes the incoming wave 2, and arrives at these overlapping portions. Wave components S12 and S21 remain.

  When there is an overlapping portion with the transition region on the high frequency side, the component S12 of the incoming wave 2 that should pass through the subband filter BF2 also passes through the subband filter BF1, and there is an overlapping portion with the transition region on the low frequency side. In this case, the component S21 of the incoming wave 1 that should pass through the subband filter BF1 also passes through the subband filter BF2. In this case, the output of the frequency interpolation filter unit 4 becomes higher than the desired signal level by the amount of the incoming wave component remaining in the overlapping portion, and a correct transmission path estimation result cannot be obtained. This inconvenience may occur even when there are overlapping portions of passbands or when there are overlapping portions of transition regions.

Therefore, in the present invention, when there is an overlapping portion other than the stop band in the frequency characteristics between the subband filters that pass adjacent subbands, the subbands are determined so that these subbands become one subband. fix.
Here, the case where the subband temporary determination unit 62 determines, for example, the subband shown in FIG. 12A will be specifically described. When the result of FIG. 12A is input, the filter type control unit 63 refers to the table data of FIG. 10B and selects an optimal subband filter. In the subband a in FIG. 12A, the IFFT index width of the passband IFFT index in the range from 4 to 16 is 12, so the subband filter C in FIG. 10B is selected. On the other hand, for the subbands b and c, the subband filter A having an IFFT index width of 2 and a passband IFFT index width of 5 is selected.

When configuring a desired bandpass filter that passes a subband from a subband filter (low-pass filter), the center frequency of the passband of the subband filter is adjusted to the center position of the subband.
For example, the subband b is centered on the IFFT index 42. When the center frequency of the passband of the subband filter A is adjusted to this, the passband of the subband filter A that passes the subband b is from IFFT index 40. There are up to 44 sections.
The subband c is centered on the IFFT index 46, and when the center frequency of the passband of the subband filter A is adjusted to this, the passband of the subband filter A that passes the subband c has an IFFT index of 44. There are up to 48 sections.
Accordingly, the passbands of the two filters overlap at the IFFT index 44.

  In this case, the filter type control unit 63 re-determines the subband as shown in FIG. That is, by newly determining the subband b including the subband c, the subband b is set to an interval from IFFT index 41 to 47, and the subband c is not applied. Thereafter, since the IFFT index width of the new subband b is 6, the filter type control unit 63 newly selects the subband filter B with reference to the table data of FIG.

  Since the new subband b has an IFFT index of 41 to 47, its center IFFT index is 44. That is, if the passband of the subband filter B is frequency shifted by IFFT index 0 to 10, the center frequency of the passband of the subband filter B coincides with the center of the new subband b. Therefore, the shift control unit 64 determines that the passband shift amount (IFFT index) is 44. The determination result is shown in FIG.

As described above, according to the first embodiment, it can be realized with a simple configuration in which the passband of the subband determined by the passband determination unit 6 is set in the frequency interpolation filter unit 4.
In addition, since a subband filter is configured for each subband, it is possible to accurately suppress noise components in the transmission path and improve reception performance.
Furthermore, if there is an overlapping part other than the stopband in the frequency characteristics between the subband filters that pass adjacent subbands, the subbands that include these subbands are determined. Are not detected redundantly, and reception performance can be improved.

  Further, according to the first embodiment, the frequency interpolation filter unit 4 includes the subband filter units 41a to 41c having different bandwidths, and the passband determination unit 6 receives the subband filter units 41a to 41c from the subband filter units 41a to 41c. Select a filter that passes the band and set its passband. By configuring in this way, it is possible to obtain a desired frequency characteristic with a much simpler configuration than that of Patent Document 2.

  Furthermore, according to the first embodiment, the incoming wave component can be passed accurately by matching the center frequency of the passband of the subband filter with the center of the subband.

Embodiment 2. FIG.
FIG. 13 is a block diagram showing the configuration of the frequency interpolation filter unit according to Embodiment 2 of the present invention, and it is possible to realize three band-pass filters that respectively allow a maximum of three subbands to pass through. As illustrated in FIG. 13, the frequency interpolation filter unit 4 </ b> A includes filter coefficient generation units 42 a to 42 c, a filter processing unit 44, and a filter coefficient addition unit 45.
In FIG. 13, the same components as those in FIG.

The filter processing unit 44 is a filter for setting a pass band based on the filter coefficients added by the filter coefficient adding unit 45 and band-limiting the output signal of the time interpolation filter unit 3.
The filter coefficient addition unit 45 adds the generated filter coefficients to the filter coefficient generation units 42a to 42c. Specifically, the filter coefficients output from the filter coefficient generation units 42a to 42c are added for each filter tap coefficient and output. The output of the filter coefficient adding unit 45 is a transmission path estimation value in which a signal component of a desired subband is passed and a noise component is suppressed.

  As described above, according to the second embodiment, the frequency interpolation filter unit 4A sets the filter coefficient for shifting the frequency of the pass band of the filter selected based on the filter type control information based on the shift control information. Based on the filter coefficients added by the filter coefficient adding section 45, the filter coefficient adding section 45 for adding the filter coefficients generated by the filter coefficient generating sections 42a to 42c to be generated, and the filter coefficients generated by the filter coefficient generating sections 42a to 42c. And a filter processing unit 44 that limits the band of the output signal of the time interpolation filter unit 3 and outputs it to the equalization unit 7. With this configuration, the same function as that of the frequency interpolation filter unit 4 according to the first embodiment can be obtained, and the circuit scale or the calculation amount can be reduced as compared with the configuration.

  In the present invention, within the scope of the invention, any combination of each embodiment, any component of each embodiment can be modified, or any component can be omitted in each embodiment. .

  Since the receiving apparatus according to the present invention can improve the reception performance by accurately suppressing the noise component of the transmission path with a simple configuration, for example, a vehicle-mounted receiver that receives digital terrestrial broadcasting using the OFDM method It is suitable for.

  1 Fourier transform unit, 2 pilot carrier extraction unit, 3 time interpolation filter unit, 4,4A frequency interpolation filter unit, 5 delay profile detection unit, 6 passband determination unit, 7 equalization unit, 41a to 41c subband filters , 42a to 42c filter coefficient generation unit, 43 output addition unit, 44 filter processing unit, 45 filter coefficient addition unit, 61 incoming wave component detection unit, 62 subband tentative determination unit, 63 filter type control unit, 64 shift control unit 421 Filter coefficient selection unit 422 Passband shift unit.

Claims (6)

A receiving apparatus for receiving an OFDM signal to which a known pilot carrier is assigned in a time direction and a frequency direction,
A Fourier transform unit that outputs a received signal by discrete Fourier transform for each OFDM symbol; and
A pilot carrier extraction unit that extracts and outputs a signal corresponding to the pilot carrier from the output signal of the Fourier transform unit;
A time interpolation filter unit for interpolating in a time direction and outputting a transmission path characteristic for the pilot carrier estimated based on an output signal of the pilot carrier extraction unit;
A delay profile detector that detects and outputs a delay profile of the transmission path from the output signal of the time interpolation filter;
Based on the output signal of the delay profile detection unit, an incoming wave component of the transmission path is detected, a subband including the incoming wave component is determined, and a frequency characteristic between filters that respectively pass the adjacent subbands is determined. When there is an overlapping portion other than the stopband, a passband determining unit that determines a subband including each of these subbands;
A frequency for setting a pass band through which the subband determined by the passband determination unit is passed, and band-limiting the output signal of the time interpolation filter unit to interpolate the transmission path characteristic for the pilot carrier in the frequency direction An interpolation filter unit;
A receiving apparatus comprising: an equalization unit that divides an output signal of the Fourier transform unit by an output signal of the frequency interpolation filter unit and performs demodulation for each subcarrier. The passband determination unit
An arrival wave component detection unit that detects the presence and absence of the arrival wave component and an arrival time difference based on an output signal of the delay profile detection unit;
A subband provisional determination unit that determines a subband including the incoming wave component detected by the incoming wave component detection unit;
Generates filter type control information for selecting a filter having a bandwidth that can pass through the subband determined by the subband provisional determination unit, and inhibits frequency characteristics between the filters that pass through adjacent subbands. If there is an overlapping part other than the band, a filter type control unit that generates filter type control information for selecting a filter having a bandwidth that can pass through the subbands including these subbands, and
A shift control unit that generates shift control information for frequency-shifting the passband of the filter selected based on the filter type control information according to the subband,
The frequency interpolation filter unit is
The receiving apparatus according to claim 1, wherein a pass band for passing the subband is set based on the filter type control information and the shift control information. The frequency interpolation filter unit is
A plurality of filters having different bandwidths;
A filter coefficient generation unit that generates a filter coefficient for frequency-shifting the pass band of the filter selected based on the filter type control information based on the shift control information;
An output addition unit that adds a result obtained by band-limiting the output signal of the time interpolation filter unit with a filter in which a pass band is set based on the filter coefficient among the plurality of filters, and outputs the result to the equalization unit; The receiving apparatus according to claim 2, further comprising: The frequency interpolation filter unit is
A plurality of filter coefficient generation units for generating a filter coefficient for frequency-shifting the passband of the filter selected based on the filter type control information based on the shift control information;
A filter coefficient adder for adding the filter coefficients generated in the plurality of filter coefficient generators;
And a filter configured to set a pass band based on the filter coefficient added by the filter coefficient adding unit, band-limit an output signal of the time interpolation filter unit, and output the band signal to the equalization unit. Item 3. The receiving device according to Item 2.   3. The shift control unit according to claim 2, wherein the shift control unit generates, as the shift control information, information for adjusting a center frequency of a pass band of a filter selected based on the filter type control information to a center of the subband. Receiver device. A reception method for receiving an OFDM signal to which a known pilot carrier is allocated in a time direction and a frequency direction,
A Fourier transform unit for performing discrete Fourier transform on the received signal for each OFDM symbol and outputting the received signal;
A pilot carrier extraction unit that extracts and outputs a signal corresponding to the pilot carrier from an output signal of the Fourier transform unit;
A step of a time interpolation filter unit interpolating in a time direction a transmission line characteristic for the pilot carrier estimated based on an output signal of the pilot carrier extraction unit;
A delay profile detection unit detecting and outputting a delay profile of a transmission line from an output signal of the time interpolation filter unit; and
A passband determination unit detects an incoming wave component of the transmission path based on an output signal of the delay profile detection unit, determines a subband including the incoming wave component, and passes each adjacent subband. If there is an overlap other than the stopband in the frequency characteristics between the filters, determining a subband including each of these subbands;
The frequency interpolation filter unit sets a pass band for passing the subband determined by the passband determination unit, band-limits the output signal of the time interpolation filter unit, and sets transmission path characteristics for the pilot carrier. Interpolating in the frequency direction;
A reception method comprising: an equalization unit that divides an output signal of the Fourier transform unit by an output signal of the frequency interpolation filter unit and performs demodulation for each subcarrier.

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