JP5647871B2 - OFDM signal retransmission apparatus - Google Patents

Description

  The present invention relates to an OFDM signal receiving apparatus for digital broadcasting and digital transmission using an OFDM (Orthogonal Frequency Division Multiplexing) system, and in particular, a delay that becomes a problem when receiving radio waves in digital broadcasting or wireless LAN. The present invention relates to an OFDM signal retransmission apparatus capable of correctly receiving and retransmitting transmission data even in an environment where a multipath whose time exceeds a GI (Guard Interval) length is received.

  FIG. 8 is a block diagram showing a configuration of a normal OFDM signal receiving apparatus. This OFDM signal receiving apparatus 200 includes a frequency converter 201 that converts a received OFDM signal into an intermediate frequency signal (IF signal), an A / D converter 202 that performs analog-digital conversion on the IF signal, and a digital IF signal. An orthogonal demodulator 203 that demodulates an equivalent baseband signal, a GI remover 204 that detects and removes GI from the equivalent baseband signal, and a predetermined FFT (Fast Fourier Transform) for the equivalent baseband signal subjected to GI removal ) FFT unit 205 that performs FFT processing with a window size and converts it to a frequency domain signal; channel estimation unit 206 that estimates a channel response from a carrier symbol of a frequency domain signal input from FFT unit 205 using a pilot signal; The frequency domain signal output from the FFT unit 205 using the estimated channel response A channel equalization unit 207 for equalization, a demapping unit 208 for performing demapping in accordance with a predetermined modulation method for the frequency domain signal subjected to channel equalization, and a parallel data signal obtained by demapping is converted into a serial data signal And a parallel-serial conversion unit 209 that restores the signal of the transmission source bit string.

  That is, the normal OFDM signal receiving apparatus 200 can perform channel equalization by the channel equalization unit 207 when the delay spread of the transmission path from the transmission source to the reception point is within the GI length. On the other hand, the normal OFDM signal receiving apparatus 200 does not have a function of equalizing a delayed wave exceeding the GI length. Therefore, when the delay spread of the channel exceeds the GI length, reception characteristics due to occurrence of inter-symbol interference and inter-carrier interference. Will be significantly impaired.

  On the other hand, there is an OFDM signal receiving apparatus having a mechanism for canceling multipath in the time domain. FIG. 9 is a block diagram showing a configuration of an OFDM signal receiving apparatus capable of equalizing a multipath whose delay time exceeds the GI length. The OFDM signal receiving apparatus 300 includes a frequency converter 301 that converts a received OFDM signal into an intermediate frequency signal (IF signal), an A / D converter 302 that performs analog-digital conversion on the IF signal, and a digital IF signal. A quadrature demodulator 303 that demodulates to an equivalent baseband signal, a subtractor 304 that cancels multipath, an adaptive filter 305 that generates a multipath replica, and an equivalent baseband signal that has undergone GI removal are subjected to predetermined processing. An FFT unit 306 that performs FFT processing with an FFT window size and converts the signal into a frequency domain signal; a channel estimation unit 307 that estimates a channel response from a carrier symbol of a frequency domain signal input from the FFT unit 306 using a pilot signal; The frequency output from the FFT unit 306 using the estimated channel response A channel equalization unit 308 that equalizes the region signal, a demapping unit 309 that performs demapping according to a predetermined modulation method on the frequency domain signal subjected to channel equalization, and a parallel data signal obtained by demapping is converted into serial data A parallel-serial conversion unit 313 that converts the signal into a signal and restores the signal of the transmission source bit string, a mapping unit 310 that maps a parallel data signal obtained by demapping and reproduces a carrier symbol, and an FFT unit 306 A division unit 311 for calculating a frequency characteristic after equalization by dividing the frequency domain signal to be divided by a carrier symbol output from the mapping unit 310, and an impulse obtained by removing the main wave component using the frequency characteristic after equalization Generating a response and allowing the adaptive filter 305 to adaptively determine the filter coefficients And a filter coefficient controller 312.

  That is, the OFDM signal receiving apparatus 300 having a mechanism for canceling multipaths in the time domain provides the adaptive filter 305 with an impulse response excluding the main wave component from the channel response from the transmission source to the reception point, and thereby It is possible to cancel the pass. However, the OFDM signal receiving apparatus 300 has a problem that the order of the filter coefficient in the adaptive filter has to be increased in order to equalize a multipath having a longer delay time. Further, in order to equalize a multipath (preceding wave) that arrives earlier than the main wave, there is a problem that an adaptive filter is required in addition to the configuration of FIG.

  In addition, the OFDM signal receiving apparatus shown in FIG. 9 cancels multipaths in the time domain, whereas an OFDM signal receiving apparatus that equalizes multipaths in the frequency domain is known (see, for example, Patent Document 1). . The conventional OFDM signal receiver shown in Patent Document 1 can equalize multipaths exceeding a guard interval of a size that cannot be received by the normal OFDM signal receiver 200 shown in FIG. The problem of having to increase the order of the filter coefficient in the adaptive filter can be solved.

  There is a relay apparatus that constitutes an OFDM signal retransmission apparatus 100 capable of equalizing multipaths exceeding GI in the frequency domain. FIG. 7 is a block diagram showing a schematic configuration of a conventional OFDM signal retransmission apparatus capable of equalizing a multipath whose delay time exceeds the GI length.

  An OFDM signal retransmission apparatus 100 shown in FIG. 7 receives a OFDM signal transmitted from a predetermined transmission source via a reception antenna 101 and removes an unnecessary signal component outside the frequency band of a desired wave. A frequency conversion unit 103, an A / D conversion unit 104, an orthogonal demodulation unit 105, a frequency domain equalization unit 106, an OFDM demodulation unit 107, an equalization coefficient calculation unit 108, a carrier symbol selection unit 109, IFFT section 110, GI adding section 111, orthogonal modulation section 112, D / A conversion section 113, frequency conversion section 114, bandpass filter 115, and transmission antenna 116.

  The frequency conversion unit 103, the A / D conversion unit 104, and the orthogonal demodulation unit 105 correspond to the frequency conversion unit 301, the A / D conversion unit 302, and the orthogonal demodulation unit 303 shown in FIG. The frequency domain equalization unit 106 is a functional unit that performs adaptive equalization in the frequency domain, and obtains an equalization error from the frequency domain signal obtained from the subsequent OFDM demodulation unit 107, and performs equalization coefficient calculation. It is controlled by the coefficient calculation unit 108. The OFDM demodulation unit 107 corresponds to a processing unit including a channel estimation unit 307, a channel equalization unit 308, and a demapping unit 309. The equalization coefficient calculation unit 108 corresponds to a processing unit including the mapping unit 310, the division unit 311, and the filter coefficient control unit 312 illustrated in FIG.

  Carrier symbol selection section 109 receives carrier symbols after channel equalization obtained from OFDM demodulation section 107, and carrier symbols obtained from a mapping section (corresponding to mapping section 310 shown in FIG. 9) in equalization coefficient calculation section 108. It is a functional unit that performs switching.

  IFFT section 110 performs inverse FFT processing on the input carrier symbol and converts it to a digital time domain signal.

  The GI adding unit 111 adds a GI to the converted digital time domain signal.

  The quadrature modulation unit 112 performs predetermined quadrature modulation on the digital time domain signal to which the GI is added.

  The D / A converter 113 converts the digital time domain signal subjected to quadrature modulation into an analog time domain signal.

  The frequency converter 114 converts the analog time domain signal into a radio frequency signal (RF signal) and generates an OFDM signal to be retransmitted.

  The bandpass filter 115 has a function of removing an extra band when retransmitting via the transmission antenna 116.

  That is, in the OFDM signal retransmission apparatus 100 shown in FIG. 7, the reception signal output from the reception antenna 101 is input to the bandpass filter 102 through a feeder cable (not shown), and is unnecessary outside the frequency band of the desired wave. Signal components are removed. The output signal of the band-pass filter 102 is input to the frequency conversion unit 103, subjected to AGC (automatic gain control) so that the output level becomes constant, and then frequency-converted.

  The parallel data output from the demapping unit (corresponding to the demapping unit 309) included in the OFDM demodulating unit 107 is input to the remapping unit (corresponding to the mapping unit 310), and carrier symbols are reproduced. One of the reproduction symbol output from the remapping unit or the carrier symbol after channel equalization output from the channel equalization unit (corresponding to the channel equalization unit 308) is selected, and a transmission symbol is output. The output of carrier symbol selection section 109 is input to IFFT section 110.

  IFFT section 110 performs IFFT processing on the carrier symbol output from carrier symbol selection section 109 and converts it to a time domain signal. The GI adding unit 111 adds a GI to the head of the OFDM symbol and sends it to the orthogonal modulation unit 112.

  The quadrature modulation unit 112 performs quadrature modulation processing on the input equivalent baseband signal, converts it to a digital IF signal, and outputs it. The digital IF signal output from the quadrature modulation unit 112 is converted into an IF signal by the D / A conversion unit 113 and output. The IF signal output from the D / A converter 1113 is frequency-converted to the RF band by the frequency converter 114, and is amplified and output so as to have a constant level. The RF signal output from the frequency converter 114 is input to the bandpass filter 115, and unnecessary radiation components outside the band are removed. The transmission signal from which unnecessary components outside the band are removed by the band-pass filter 115 is supplied to the transmission antenna 116 through a feeder cable (not shown) and radiated as a radio wave.

  Note that the threshold determination process by demapping and remapping is a process of replacing with a known transmission symbol closest to the input carrier symbol. This process has the advantage of eliminating equalization errors and white noise, but may not be necessary.

  Here, consider an environment in which a multilevel GI multipath with a high level is received. In such a reception environment, since the signal power of the received signal is significantly reduced by the subcarrier, the error rate of the signal transmitted by the subcarrier increases. About this data error, it is known that the reception characteristic can be improved by erasing or performing reliability weighting in error correction.

JP 2004-343546 A

  When retransmitting an OFDM signal using the conventional OFDM signal retransmitting apparatus 100 in a reception environment where a multipath within a GI with a large level is received, the OFDM signal retransmitting apparatus 100 reduces all the distortions of the propagation path. Because of equalization, the information on the propagation path that was received when the signal was received by the OFDM signal retransmission apparatus 100 is lost. Therefore, a receiving apparatus (for example, see FIG. 8) that receives a signal retransmitted by the OFDM signal retransmitting apparatus 100 cannot use propagation path information when performing error correction decoding. There was a problem that further improvement could not be expected.

  The present invention has been made to solve such a problem, and the object of the present invention is to improve the signal quality of the multipath whose delay time exceeds the GI on the receiving side even in an environment where a multi-level GI multipath is received at a high level. An object of the present invention is to provide an OFDM signal retransmission apparatus that retransmits an OFDM signal so that degradation of the signal can be improved.

The OFDM signal retransmission apparatus according to the first aspect of the present invention is an OFDM signal retransmission apparatus for adaptively retransmitting an OFDM signal of a transmission source, and an input OFDM signal is converted into an FFT window size of the OFDM signal. FFT processing is performed with a size that is a power of 2 and converted to a frequency domain signal. A signal obtained by equalizing frequency characteristic distortion due to multipath exceeding the GI length is equalized to the FFT window size of 2 for the frequency domain signal . A frequency domain equalization unit that converts to a time domain signal by performing IFFT processing with a power-multiplied size, and a time domain signal obtained from the frequency domain equalization unit is subjected to FFT processing with an FFT window size of the OFDM signal to obtain a frequency into a region signal, the OFDM demodulation unit that performs channel equalization with respect to the frequency-domain signal, is input from the OFDM demodulator An equalization coefficient calculation unit for calculating an equalization coefficient of the frequency domain equalization unit from an equalization error signal obtained using a frequency domain signal, a channel response, and a reproduction symbol, and the frequency domain equalization unit An OFDM symbol extraction unit that extracts an OFDM symbol from a time domain signal, and a retransmission signal generation unit that generates an OFDM signal to be retransmitted from the OFDM symbol.

An OFDM signal retransmission apparatus according to a second aspect of the present invention is an OFDM signal retransmission apparatus that adaptively retransmits an OFDM signal as a transmission source, and converts an input OFDM signal into an FFT window size of the OFDM signal. FFT processing is performed with a size that is a power of 2 and converted to a frequency domain signal. A signal obtained by equalizing frequency characteristic distortion due to multipath exceeding the GI length is equalized to the FFT window size of 2 for the frequency domain signal . A frequency domain equalization unit that converts to a time domain signal by performing IFFT processing with a power-multiplied size, and a time domain signal obtained from the frequency domain equalization unit is subjected to FFT processing with an FFT window size of the OFDM signal to obtain a frequency into a region signal, the OFDM demodulation unit that performs channel equalization with respect to the frequency-domain signal, is input from the OFDM demodulator An equalization coefficient calculation unit for calculating an equalization coefficient of the frequency domain equalization unit from an equalization error signal obtained using a frequency domain signal, a channel response, and a reproduction symbol, and the frequency domain equalization unit An effective symbol calculation unit that extracts an effective symbol having a time width corresponding to an effective symbol length from OFDM symbols from a time domain signal, a GI addition unit that adds a guard interval (GI) to the effective symbol, and the GI And a retransmission signal generating means for generating an OFDM signal to be retransmitted from the added effective symbol.

  According to the present invention, even in an environment where a multi-level GI multipath is received, it is possible to improve signal quality degradation due to a multipath whose delay time exceeds the GI on the receiving side.

1 is a block diagram of an OFDM signal retransmission apparatus according to a first embodiment of the present invention. It is a block diagram of the OFDM signal retransmission apparatus of Example 2 according to the present invention. (A), (b) is a figure which shows the delay profile and frequency characteristic which an OFDM signal retransmission apparatus receives. (A), (b) is a figure which shows the delay profile and frequency characteristic which the conventional OFDM signal retransmission apparatus retransmits. (A), (b) is a figure which shows the delay profile and frequency characteristic which the OFDM signal retransmission apparatus of Example 1 and Example 2 by this invention retransmits. It is a comparative example of the BER characteristic in the OFDM signal retransmission apparatus of Example 1 by this invention, and the conventional OFDM signal retransmission apparatus. It is a block diagram which shows schematic structure of the conventional OFDM signal retransmission apparatus which can equalize the multipath where delay time exceeds GI length. It is a block diagram which shows schematic structure of the conventional normal OFDM signal receiver. It is a block diagram which shows schematic structure of the conventional OFDM signal receiver which can equalize the multipath where delay time exceeds GI length.

  Hereinafter, embodiments of an OFDM signal retransmission apparatus according to the present invention will be described with reference to the drawings. First, the OFDM signal retransmission apparatus according to the first embodiment of the present invention will be described.

[Example 1]
FIG. 1 is a block diagram of an OFDM signal retransmission apparatus according to a first embodiment of the present invention. The OFDM signal retransmission apparatus 10 according to the first embodiment receives an IF signal obtained through a bandpass filter (BPF) and a frequency conversion unit (not shown) similar to those in FIG. 7 and performs A / D conversion. / D conversion unit 11, orthogonal demodulation unit 12, frequency domain equalization unit 1315 (FFT unit 13, equalization unit 14 and IFFT unit 15), OFDM demodulation unit 1923 (GI removal unit 19, FFT unit 20, channel) Equalization unit 21, channel estimation unit 22 and demapping unit 23) and equalization coefficient calculation unit 2429 (mapping unit 24, first division unit 25, second division unit 26, equalization error calculation unit 27, delay profile calculation) Unit 28 and region conversion unit 29), OFDM symbol extraction unit 16, orthogonal modulation unit 17, and D / A conversion unit 18, and then transmits the retransmission signal in the same manner as in FIG. conversion Fine band-pass filter (BPF) is applied.

  The frequency conversion on the input side (corresponding to the frequency conversion unit 103 shown in FIG. 7) converts the frequency of the input signal into an IF signal. The IF signal output from the frequency converter is input to the A / D converter 11.

  The A / D converter 11 performs A / D conversion on the input IF signal and outputs a digital IF signal. The digital IF signal output from the A / D converter 11 is input to the quadrature demodulator 12.

  The quadrature demodulation unit 12 performs quadrature demodulation on the digital IF signal input from the A / D conversion unit 11 and outputs an equivalent baseband signal. The equivalent baseband signal output from the orthogonal demodulation unit 12 is input to the frequency domain equalization unit.

  The frequency domain equalization unit 1315 equalizes the equivalent baseband signal input from the quadrature demodulation unit 12 in the frequency domain using the equalization coefficient input from the region conversion unit 29 of the equalization coefficient calculation unit, and performs time domain The equivalent baseband signal is output. The output of the IFFT unit 15 of the frequency domain equalization unit is divided into two, one being input to the GI removal unit 19 of the OFDM demodulation unit and the other being input to the OFDM symbol extraction unit 16.

  The OFDM demodulator 1923 OFDM demodulates the equivalent baseband signal, and outputs the carrier symbol after FFT, the channel response, and the parallel signal after demapping to the equalization coefficient calculator 2429.

  The equalization coefficient calculation unit 2429 calculates an equalization coefficient from the equalization error signal obtained using the carrier symbol of the frequency domain signal input from the OFDM demodulation unit 1923, the channel response, and the reproduction symbol of the parallel signal. The data is output to the equalization unit 1315.

  The OFDM symbol extraction unit 16 extracts a signal corresponding to an OFDM symbol composed of an effective symbol and a GI from the equivalent baseband signal output from the frequency domain equalization unit 1315 and inputs the signal to the orthogonal modulation unit 17.

  The orthogonal modulation unit 17 performs orthogonal modulation on the equivalent baseband signal input from the OFDM symbol extraction unit 16 and inputs the digital IF signal to the D / A conversion unit 18.

  The D / A converter 18 D / A converts the digital IF signal. The IF signal obtained by D / A conversion is subjected to frequency conversion and a band-pass filter (BPF) in the same manner as in FIG. 7 in order to transmit a retransmission signal.

  The frequency domain equalization unit 1315 includes an FFT unit 13, an equalization unit 14, and an IFFT unit 15.

  The FFT unit 13 performs an FFT process on the equivalent baseband signal input from the quadrature demodulation unit 12 with a size that is a power of 2 of the FFT window size, and is 1/2 of the carrier interval of the input OFDM signal. Convert to frequency domain signal with frequency interval.

  The equalization unit 14 equalizes the frequency characteristic distortion by dividing the frequency domain signal output from the FFT unit 13 by the equalization coefficient input from the equalization coefficient calculation unit 2429. The output of the equalization unit 14 is subjected to IFFT processing with the same size as that of the FFT unit 13, converted into a time domain signal, and an equivalent baseband signal is output to the OFDM demodulation unit 1923.

  The OFDM demodulation unit 1923 includes a GI removal unit 19, an FFT unit 20, a channel estimation unit 22, a channel equalization unit 21, and a demapping unit 23.

  The GI removal unit 19 removes the GI from the equivalent baseband signal input from the frequency domain equalization unit 1315, and outputs an equivalent baseband signal having a time width corresponding to the effective symbol period of the OFDM signal.

  The FFT unit 20 performs an FFT process on the equivalent baseband signal in the effective symbol period input from the GI removal unit 19 with the FFT window size of the OFDM signal, and converts it into a carrier symbol. The output of the FFT unit 20 is divided into three and output to the channel equalization unit 21, the channel estimation unit 22, and the equalization coefficient calculation unit 2429.

  The channel estimation unit 22 estimates a channel response from the carrier symbol input from the FFT unit 20 and outputs it. The channel response output from the channel estimation unit 22 is divided into two, and one is output to the channel equalization unit 21 and the other is output to the equalization coefficient calculation unit 2429.

  The channel equalization unit 21 divides the carrier symbol input from the FFT unit 20 by the channel response input from the channel estimation unit 22 to perform channel equalization. The equalized carrier symbol output from the channel equalization unit 21 is input to the demapping unit 23.

  The demapping unit 23 demaps the equalized carrier symbol and outputs a parallel signal. The output of the demapping unit 23 is input to the equalization coefficient calculation unit 2429.

  The equalization coefficient calculation unit 2429 includes a frequency characteristic calculation unit 2426, an equalization error calculation unit 27, a delay profile calculation unit 28, and a region conversion unit 29.

  The carrier symbol of the frequency domain signal, the channel response, and the reproduction symbol of the parallel signal input from the OFDM demodulator 1923 are input to the frequency characteristic calculator 2426 to calculate the equalized frequency characteristic. The output of the frequency characteristic calculator 2426 is input to the equalization error calculator 27.

  The equalization error calculation unit 27 subtracts 1 from the equalized frequency characteristic output from the frequency characteristic calculation unit 2426, calculates an equalization error, and generates an equalization error signal. The output of the equalization error calculation unit 27 is input to the delay profile calculation unit 28.

  The delay profile calculation unit 28 calculates a delay profile using the equalization error signal and outputs the delay profile to the region conversion unit 29. The domain transform unit 29 transforms the delay profile from the time domain to the frequency domain with a power of 2 times the FFT window size, and inputs the equalization coefficient to the frequency domain equalization unit 1315.

  The frequency characteristic calculation unit 2426 includes a mapping unit 24, a first divider 25, and a second divider 26.

  The parallel signal input from the OFDM demodulator 1923 is input to the mapping unit 24. The mapping unit 24 maps the parallel signal and outputs the carrier symbol to the first divider 25.

  The first divider 25 calculates the equalized frequency characteristic by dividing the carrier symbol input from the OFDM demodulator 1923 by the carrier symbol input from the mapping unit 24 and outputs the calculated frequency characteristic to the second divider 26. .

The second divider 2 6 is divided by the channel response to be input to the frequency characteristic of the equalized input from the first divider 25 from the OFDM demodulator 1923, distortion caused by GI in a multi-path is separated The frequency characteristic is output to the equalization error calculation unit 27.

  The delay profile calculation unit 28 can be realized by an existing method. For example, the delay profile calculation unit 28 performs an IFFT process on the equalization error signal input from the equalization error calculation unit 27 to obtain an equalization error signal in the time domain. An IFFT unit to be converted, an adaptive coefficient multiplier for multiplying a time domain equalization error signal obtained from the IFFT unit by a predetermined adaptive coefficient, and a time domain equalization error signal input from the adaptive coefficient multiplier The delay profile can be configured by adding a delay profile subjected to so-called leak processing for adjusting the delay profile to be sequentially calculated by delaying the unit by a unit update time (not shown). ). The equalization error signal is an error signal obtained by subtracting 1 from the result of dividing the frequency domain signal before channel equalization processing by the frequency domain signal after symbol reproduction. In this case, the domain transform unit 29 performs an FFT process for transforming the delay profile obtained from the delay profile calculation unit 28 from the time domain to the frequency domain at a power of 2 times the FFT window size, and equalizes the frequency domain. The coefficient is sent to the frequency domain equalization unit 1315.

  Further detailed description of the OFDM demodulating unit 1923 is omitted because it is a known technique. Further, the frequency domain equalization unit 1315, the frequency characteristic calculation unit 2426 of the equalization coefficient calculation unit 2429, the equalization error calculation unit 27, the delay profile calculation unit 28, and the region conversion unit 29 are equal in the frequency domain, not in the time domain. The technique of patent document 1 can also be applied.

  However, the OFDM signal retransmission apparatus 10 of the present embodiment includes an equalization unit 14 in the frequency domain equalization unit 1315 (hereinafter referred to as a “first equalization unit”) and a channel equalization unit 21 in the OFDM demodulation unit 1923. (Hereinafter referred to as “second equalization unit”) has two equalization functional blocks. However, unlike the conventional configuration shown in FIG. 7, it is transmitted to the outside using a signal output from the OFDM demodulation unit 1923. The retransmission signal to be transmitted to the outside is generated using the signal output from the IFFT unit 15 of the frequency domain equalization unit 1315.

  The first equalization unit (equalization unit 14) equalizes frequency characteristic distortion due to multipath with a delay time exceeding GI. A normal OFDM signal receiving apparatus 200 as shown in FIG. 8 does not have a function equivalent to that of the first equalization unit (equalization unit 14). This process is also necessary for retransmission.

  On the other hand, the second equalization unit (channel equalization unit 21) equalizes the frequency characteristic distortion obtained by the channel estimation unit 22 using the pilot signal. A normal OFDM signal receiving apparatus 200 as shown in FIG. 8 is provided with a channel equalization unit 207 having a function equivalent to that of the first equalization unit.

  Therefore, for example, when there is no major deterioration factor between the OFDM signal retransmission apparatus provided in the case of retransmission at home and the normal OFDM signal reception apparatus 200 that receives the retransmission signal, the OFDM signal It is not always necessary to perform channel equalization by the second equalization unit in the retransmission apparatus. Rather, the retransmission of OFDM signals under such circumstances has the following problems.

  For example, consider an environment in which a multilevel GI multipath is received. In such a reception environment, since the signal power of the received signal is significantly reduced by the subcarrier, the error rate of the signal transmitted by the subcarrier increases. Therefore, the reception performance can be further improved by equalizing the multipath propagation path characteristics in the GI on the receiving apparatus side without equalizing on the OFDM signal retransmission apparatus side. In the normal OFDM signal receiving apparatus 200, it is possible to improve reception characteristics by eliminating or performing reliability weighting in an error correction unit (not shown) that operates in cooperation with the channel equalization unit 207. It has been known.

  That is, assuming that the delay profile and frequency characteristics of the signal received by the OFDM signal retransmission apparatus have characteristics as shown in FIG. 3, the conventional OFDM signal retransmission apparatus 100 as shown in FIG. As shown in FIG. 2, in order to equalize the multipath propagation path characteristics within and outside the GI, the normal OFDM signal receiving apparatus 200 performs error correction processing using the multipath propagation path characteristics within the GI. I can't. On the other hand, according to the OFDM signal retransmission apparatus 10 of the first embodiment, the multipath propagation path characteristics in the GI are equalized on the receiving apparatus side without being equalized on the OFDM signal retransmission apparatus side. (Refer to FIG. 5), when performing error correction processing in the conventional OFDM signal retransmitting apparatus 100 as shown in FIG. 8, the multipath propagation path characteristics in the GI can be used, and the reception performance can be further improved. .

FIG. 6 is a comparative example of BER characteristics in the OFDM signal retransmission apparatus according to the first embodiment of the present invention and the conventional OFDM signal retransmission apparatus. In other words, FIG. 6 shows an example of the receiver with respect to the C / N of the input signal of the OFDM signal retransmission apparatus obtained by computer simulation assuming that the retransmission signal output from the OFDM signal retransmission apparatus is received by the receiver. The bit error rate characteristics after code correction are shown. However, it is assumed that a delay wave (within GI) with a delay time of 10 μs and D / U of 1 dB and a delay wave with a delay time of 200 μs and D / U of 15 dB (outside the GI) are received. When the conventional OFDM signal retransmission apparatus 100 is used, even if C / N is sufficiently large, it does not fall below the required BER (2 × 10 ⁻⁴ ), so reception is impossible. When the transmission device 10 is used, it can be seen that if the C / N increases, the required BER falls below and reception is possible. This effect is the same when the OFDM signal retransmission apparatus 50 according to the second embodiment described below is used.

  Next, an OFDM signal retransmission apparatus according to the second embodiment of the present invention will be described. Similar components are denoted by the same reference numerals.

[Example 2]
FIG. 2 is a block diagram of an OFDM signal retransmission apparatus according to a second embodiment of the present invention. The OFDM signal retransmission apparatus 50 according to the second embodiment receives an IF signal obtained through a bandpass filter (BPF) and a frequency conversion unit (not shown) similar to those in FIG. 7 and performs A / D conversion. / D conversion unit 11, orthogonal demodulation unit 12, frequency domain equalization unit 1315 (FFT unit 13, equalization unit 14 and IFFT unit 15), OFDM demodulation unit 1923 (GI removal unit 19, FFT unit 20, channel) Equalization unit 21, channel estimation unit 22 and demapping unit 23) and equalization coefficient calculation unit 2429 (mapping unit 24, first division unit 25, second division unit 26, equalization error calculation unit 27, delay profile calculation) Unit 28 and region conversion unit 29), effective symbol calculation unit 51, GI addition unit 52, quadrature modulation unit 17, and D / A conversion unit 18, and then transmits a retransmit signal. Same as 7 , Frequency conversion and band-pass filter (BPF) is performed.

  Compared with the OFDM signal retransmission apparatus 10 of the first embodiment shown in FIG. 1 and the OFDM signal retransmission apparatus 50 of the second embodiment shown in FIG. 2, the second embodiment is effective in place of the OFDM symbol extraction unit 16. The difference is that a symbol extraction unit 51 and a GI addition unit 52 are provided.

  The effective symbol extraction unit 51 extracts and outputs an equivalent baseband signal having a time width corresponding to an effective symbol period from the equivalent baseband signal input from the frequency domain equalization unit 1315. At this time, it is not always necessary to extract a signal in a period corresponding to an effective symbol, and a GI may be included.

  The GI adding unit 52 adds the same signal as the end of the equivalent baseband signal input from the effective symbol extracting unit 51 as the GI to output.

  In the first embodiment, an OFDM symbol that combines the effective symbol period and the GI is extracted and used as a retransmission signal. Therefore, compared with the configuration of the second embodiment, the configuration of the first embodiment has an advantage that the GI adding unit 52 is unnecessary, but when there is an error in the timing for OFDM symbol extraction, the retransmission signal May include unnecessary discontinuities.

  Therefore, in the second embodiment, GI is added to the signal corresponding to the effective symbol period and this is used as the retransmitted signal. Therefore, the effective symbol period is extracted in consideration of the timing error when extracting the effective symbol period. This is advantageous in that it eliminates unnecessary discontinuities in the retransmitted signal by extracting the continuous symbols including the GI and extending the cycle by advancing the timing.

  According to the OFDM signal retransmission apparatus 50 of the second embodiment of the present invention, not only the effects described with reference to FIGS. 3 to 6 can be obtained, but also the accuracy of extracting effective symbol periods can be increased on the receiving apparatus side. It becomes like this.

  According to the present invention, it is possible to improve signal quality degradation due to a multipath whose delay time exceeds the GI on the receiving side even in an environment where a large level GI multipath is received. Useful for receiver applications.

DESCRIPTION OF SYMBOLS 10 OFDM signal retransmission apparatus 11 A / D conversion part 12 Orthogonal demodulation part 13 FFT part 14 Equalization part 15 IFFT part 16 OFDM symbol extraction part 17 Orthogonal modulation part 18 D / A conversion part 19 GI removal part 20 FFT part 21 Channel Equalization unit 22 Channel estimation unit 23 Demapping unit 24 Mapping unit 25 First division unit 26 Second division unit 27 Equalization error calculation unit 28 Delay profile calculation unit 29 Region conversion unit 50 OFDM signal retransmission apparatus 51 Effective symbol extraction unit 52 GI Addition Unit 1315 Frequency Domain Equalization Unit 1923 OFDM Demodulation Unit 2429 Equalization Coefficient Calculation Unit

Claims (2)

An OFDM signal retransmission apparatus that adaptively equalizes and retransmits a transmission source OFDM signal,
The input OFDM signal is converted into a frequency domain signal by performing FFT processing with a size that is a power of 2 of the FFT window size of the OFDM signal, and the frequency characteristic distortion of the frequency domain signal due to multipath exceeding the GI length and the frequency domain equalization unit which converts the IFFT processing to a time domain signal at an equalized signal, a power of two times the size of the FFT window size,
An OFDM demodulator for performing a time domain signal obtained from the frequency domain equalization unit, performing FFT processing on the FFT window size of the OFDM signal to convert it to a frequency domain signal , and performing channel equalization on the frequency domain signal; ,
An equalization coefficient calculation unit for calculating an equalization coefficient of the frequency domain equalization unit from an equalization error signal obtained using the frequency domain signal, the channel response and the reproduction symbol input from the OFDM demodulation unit;
An OFDM symbol extraction unit for extracting an OFDM symbol from the time domain signal obtained from the frequency domain equalization unit;
Retransmission signal generating means for generating an OFDM signal to be retransmitted from the OFDM symbol;
An OFDM signal retransmission apparatus comprising: An OFDM signal retransmission apparatus that adaptively equalizes and retransmits a transmission source OFDM signal,
The input OFDM signal is converted into a frequency domain signal by performing FFT processing with a size that is a power of 2 of the FFT window size of the OFDM signal, and the frequency characteristic distortion of the frequency domain signal due to multipath exceeding the GI length and the frequency domain equalization unit which converts the IFFT processing to a time domain signal at an equalized signal, a power of two times the size of the FFT window size,
An OFDM demodulator for performing a time domain signal obtained from the frequency domain equalization unit, performing FFT processing on the FFT window size of the OFDM signal to convert it to a frequency domain signal , and performing channel equalization on the frequency domain signal; ,
An equalization coefficient calculation unit for calculating an equalization coefficient of the frequency domain equalization unit from an equalization error signal obtained using the frequency domain signal, the channel response and the reproduction symbol input from the OFDM demodulation unit;
An effective symbol calculation unit that extracts an effective symbol having a time width corresponding to an effective symbol length among OFDM symbols from the time domain signal obtained from the frequency domain equalization unit;
A GI adding unit for adding a guard interval (GI) to the effective symbol;
Retransmission signal generation means for generating an OFDM signal to be retransmitted from the effective symbol to which the GI is added;
An OFDM signal retransmission apparatus comprising:

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