JPWO2008139624A1 - OFDM transmitter and OFDM receiver - Google Patents

Abstract

An OFDM transmitting apparatus and OFDM receiving apparatus capable of improving transmission efficiency while maintaining good BER characteristics even in a wireless communication system in which communication is performed between a plurality of wireless communication apparatuses having various communication capabilities. In the wireless terminal device (100), a setting state balance determination unit (170) that determines the balance between the symbol length of the received OFDM signal and the selected section, and when the selected section is shorter than the symbol length, the received Fourier transform section, the received OFDM signal And a feedback information generation unit (180) for generating feedback information to the transmission side including the maximum delay time and the spread of the impulse response in the frequency domain equalization process. As a result, the symbol length can be adjusted on the transmission side using the feedback information, so that it is possible to prevent a decrease in BER that occurs in the wireless terminal device (100) on the reception side due to imbalance in the setting state.

Description

  The present invention relates to an OFDM transmitter and an OFDM receiver.

  In recent years, wireless transmission schemes suitable for high-speed packet transmission have been studied. For this high-speed packet transmission, it is necessary to widen the use frequency band. It is known that when broadband transmission is performed by mobile communication, the communication channel becomes a frequency selective channel composed of a plurality of paths having different delay times. Therefore, in wideband transmission in mobile communication, as shown in FIG. 1, intersymbol interference (ISI: Inter Symbol Interference) in which the preceding symbol interferes with the subsequent symbol occurs. When this intersymbol interference occurs, the bit error rate (BER) characteristics deteriorate. Further, since the frequency selective channel is a channel whose channel transfer function varies within the frequency band, the spectrum of the signal received through such a channel is distorted.

  As a technique for improving the BER by removing the influence of ISI, there is frequency domain equalization (FDE) (for example, see Non-Patent Document 1). In FDE, a received signal block is decomposed into orthogonal frequency components by Fast Fourier Transform (FFT), and each frequency component is multiplied by an equalization weight approximated to the inverse of the channel transfer function, and then inverse Fast Fourier Transform is performed. (IFFT: Inverse Fast Fourier Transform) to convert to a time domain signal. This FDE can compensate for the distortion of the spectrum of the received signal. As a result, ISI is reduced and BER characteristics are improved. As the equalization weight, a minimum mean square error (MMSE) weight that minimizes the mean square error between the equalized frequency component and transmission signal component gives the best BER characteristics.

  However, in the technique described in Non-Patent Document 1, it is necessary that the received signal can be handled as a repeated signal having an FFT block length. Here, a signal that can be expressed by combining various waveforms that can be expressed in an arbitrary n period with a basic waveform having a block length of one period is referred to as a repetitive signal. For this reason, a guard interval (GI) that adds the same signal as the tail part of the symbol block to the head of the symbol block is provided on the transmission side. However, when the GI is provided, the data transmission rate is lowered by the GI length.

Thus, there is a wireless communication device disclosed in Patent Document 1 that can improve transmission efficiency while maintaining good BER characteristics. This wireless communication apparatus includes an FFT unit 14 that performs FFT on a received signal that does not have a GI to obtain a plurality of frequency components, an FDE unit 15 that performs frequency equalization on the obtained frequency components, and a frequency domain An IFFT unit 16 that obtains a signal sequence by performing IFFT on the equalized frequency components, a selection unit 17 that selects a part of the obtained signal sequence, and an FFT unit 14 and a selection unit, respectively, A setting unit 13 to be set in the unit 17, an FFT unit 21 for performing FFT on the selected signal sequence to obtain a plurality of frequency components, a P / S unit 22 for converting the obtained frequency components into a serial sequence, And a demodulator 18 that demodulates the frequency component converted into the serial sequence. With this configuration, it is possible to increase transmission efficiency while maintaining good BER characteristics.
JP 2006-304192 A D. Falconer, SL Ariyavistakul, A. Benyamin-Seeyar, and B. Eidson, “Frequency domain equalization for single-carrier broadband wireless systems”, IEEE Commun. Mag., Vol. 40, pp.58-66, Apr. 2002 .

  By the way, there is a wireless communication system in which communication is performed between a wireless terminal having various capabilities (spec, battery remaining amount, allowable service) and a base station. When the conventional wireless communication apparatus is applied to such a wireless communication system, there is a possibility that the BER characteristic cannot be maintained. That is, in order for the above-described conventional wireless communication apparatus to be effective, the condition that the selected section is 1 OFDM symbol length or longer must be satisfied, but the wireless communication system may not be able to satisfy the condition. . As a result, there is a problem that the transmission efficiency is also lowered due to the lowered BER characteristics.

  An object of the present invention is to provide an OFDM transmission capable of improving transmission efficiency while maintaining good BER characteristics even in a wireless communication system in which communication is performed between a plurality of wireless communication devices in various communication capabilities. An apparatus and an OFDM receiver are provided.

  The OFDM receiving apparatus of the present invention is a time domain obtained by performing frequency domain equalization processing after the received OFDM signal is Fourier transformed in the Fourier transform section to be converted to a frequency domain signal, and further inverse Fourier transformed. An OFDM receiver for extracting a part of a signal as a selection section to be demodulated, wherein the balance determination means for determining the balance between the symbol length of the received OFDM signal and the selection section, and the selection section is shorter than the symbol length And a feedback information generating means for generating feedback information to the transmitting side including a Fourier transform section, a maximum delay time of the received OFDM signal, and a spread of an impulse response in the frequency domain equalization process.

  The OFDM transmission apparatus of the present invention is a time domain obtained by performing frequency domain equalization after the received OFDM signal is Fourier transformed in the Fourier transform section to be converted to a frequency domain signal, and further inverse Fourier transformed. An OFDM transmitter that transmits an OFDM signal toward an OFDM receiver that extracts a part of the signal as a selection section to be demodulated, and includes an impulse in a Fourier transform section, a maximum delay time of the received OFDM signal, and a frequency domain equalization process An acquisition means for acquiring feedback information including a response spread; and using the feedback information, the number of subcarriers to which modulation data is mapped so that a symbol length of the OFDM signal is equal to or less than a length of the selection interval. And an adjusting means for adjusting.

  According to the present invention, OFDM transmission capable of improving transmission efficiency while maintaining good BER characteristics even in a wireless communication system in which communication is performed between a plurality of wireless communication devices in various communication capabilities. An apparatus and an OFDM receiver can be provided.

Illustration of ISI Diagram for explaining distortion by ISI Operation explanatory diagram of FDE according to the embodiment of the present invention 1 is a block diagram showing a configuration of a wireless terminal device according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a configuration of a wireless terminal apparatus according to Embodiment 1 FIG. 2 is a block diagram showing a configuration of a base station apparatus according to Embodiment 1 FIG. 2 is a block diagram showing a configuration of a base station apparatus according to Embodiment 1 The figure which uses for description of the relationship between the symbol length of a state in which the setting state is balanced and the reception FFT interval The figure which uses for description of the relationship between the symbol length of a state where the setting state is not balanced and the reception FFT interval The figure which shows the state after taking the setting state balance from the state of FIG. Block diagram showing a configuration of a base station apparatus according to Embodiment 2

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the embodiments, the same components are denoted by the same reference numerals, and the description thereof will be omitted because it is redundant.

(Embodiment 1)
First, the principle of the basic operation of the FDE according to this embodiment will be described.

  As described in Patent Document 1, in this FDE, when the block length of each symbol block is Nc symbols, Nc equalization weights w (k) (k = 0 to Nc−1) are set. Use. That is, FDE is equivalent to linear filter processing with a transfer function w (k) (k = 0 to Nc−1). The impulse response of the FDE is concentrated in a narrow range around the time t = 0.

  Further, the FDE according to the present embodiment does not require a GI. For this reason, when a plurality of paths having different delays are present in the propagation path, ISI from the tail part of the previous symbol block occurs at the head part of each symbol block. For example, if the maximum value of the delay time difference between the L paths (the maximum delay amount of the delayed wave) is Δ symbols, the ISI interval is the Δ symbol interval from the beginning of the symbol block. As described above, when the ISI in the Δ symbol section is generated at the head of the symbol block, a correct frequency component cannot be obtained in the FFT, so that the signal sequence after FDE is distorted. The distortion due to the ISI spreads in time by the extent of the impulse response. In other words, the distortion due to the ISI is so small that it can be ignored at a position distant in time from the ISI interval.

  Thus, for example, assuming that the spread of the impulse response is ± M symbols, the distortion due to ISI is as shown in FIG. 2, and the distortion in the t = Δ + M to Nc−M−1 symbol section is ignored in each symbol block after FDE. It becomes small as much as possible. Therefore, as shown in FIG. 3, if only the signal in the t = Δ + M to Nc−M−1 symbol section is selected in each symbol block after FDE, distortion can be reduced without adding GI to each symbol block. A signal after no equalization can be obtained. In addition, in order to obtain a continuous equalized signal, the starting point of the FFT interval is sequentially shifted by Nc-2M-Δ symbols. In this way, by setting a plurality of FFT sections so as to overlap each other and setting a selection section shorter than each FFT section, a continuous signal without distortion can be obtained in FDE for a signal having no GI. Obtainable. In this way, FDE that does not require GI becomes possible. As a result, it is not necessary to add a GI on the transmission side, so that transmission efficiency can be improved.

  Next, a configuration of main parts of the wireless terminal device in the wireless communication system according to the present embodiment will be described.

  As shown in FIG. 4, radio terminal apparatus 100 according to Embodiment 1 includes reception radio processing section 110, setting section 120, ISI removal processing section 130, multicarrier demodulation section 140, demodulation section 150, and setting information. An acquisition unit 160, a setting state balance determination unit 170, a feedback information generation unit 180, and a transmission wireless processing unit 190 are included.

  Reception radio processing section 110 receives a multicarrier signal transmitted from a communication partner via an antenna, and performs predetermined radio reception processing (down-conversion, A / D conversion, etc.) on the received signal. The multi-carrier signal here is an OFDM signal having no GI. The signal after radio processing (reception sequence signal) is output to setting section 120 and ISI removal processing section 130.

  The setting unit 120 outputs timing information (symbol timing) obtained by performing synchronization processing using the signal after radio processing to the ISI removal processing unit 130. Further, the setting unit 120 performs an FFT interval of Nc = Ns + 2M + Δ samples to the ISI removal processing unit 130 based on the maximum delay amount of the delay wave specified using the delay profile and the spread of the impulse response of the FDE. And a selection section of the Ns symbol. Further, as illustrated in FIG. 3, the setting unit 120 sets the start point of the FFT interval and the selection interval to be set this time from the start point of the FFT interval and the selection interval set last time, by Nc−2M−Δ. Set to a timing shifted by a symbol. Here, it is assumed that the maximum delay amount of the delayed wave is Δ symbol and the spread of the impulse response of FDE is ± M symbol. Ns corresponds to the symbol length of the transmission signal that is normally transmitted by the communication partner.

  The ISI cancellation processing unit 130 performs ISI cancellation processing on the signal after the radio reception processing, and outputs the signal after ISI cancellation processing to the multicarrier demodulation unit 140.

  The ISI removal processing unit 130 includes an FFT unit 132, an FDE unit 134, an IFFT unit 136, and a selection unit 138.

  As shown in FIG. 3, the FFT unit 132 performs FFT of a size of Nc = Ns + 2M + Δ on the received signal sequence having no GI in the FFT interval set by the setting unit 120 to obtain a plurality of frequency components. The reception FFT section of the FFT unit 132 is Nc.

  The FDE unit 134 performs FDE on each frequency component by multiplying each frequency component by the MMSE equalization weight. Each frequency component after the FDE is output to the IFFT unit 136 in parallel. As the MMSE equalization weight, for example, “Takeda et al.,“ The transmission performance with space and frequency-domain process for DS-CDMA. ) ", Technical report of IEICE Technical Report, RCS2003-33, pp.21-25, 2003-05" is used.

  IFFT section 136 performs IFFT on each frequency component after FDE to obtain a signal sequence after FDE.

  The selection unit 138 selects a part of the Nc symbol signal sequence, that is, a signal sequence in the selection section set by the setting unit 120, and outputs the selected signal sequence to the multicarrier demodulation unit 140.

  As shown in FIG. 5, multicarrier demodulation section 140 includes FFT section 142, subcarrier demapping section 144, and P / S conversion section 146. The FFT unit 142 converts the signal sequence from the selection unit 138 from a time direction signal to a frequency direction signal. The subcarrier demapping unit 144 performs demapping of the signal in the frequency direction obtained by the FFT unit 142. The demapping is performed with a mapping pattern corresponding to a subcarrier mapping unit 254 described later. There may be a case where mapping is not performed. The parallel signal is output to the P / S converter 146. P / S conversion section 146 converts the parallel signal from subcarrier demapping section 144 into a serial signal, and outputs the obtained signal sequence to demodulation section 150.

  Demodulation section 150 performs demodulation processing on the signal sequence from multicarrier demodulation section 140 to obtain received data.

  The setting information acquisition unit 160 acquires the reception FFT interval and the selection interval, the maximum delay time, and the spread of the impulse response set by the setting unit 120 in the ISI removal processing unit 130 from the setting unit 120, and sets the broadcast channel of the reception signal. The included OFDM symbol length Ns on the transmission side is acquired.

  The setting state balance determination unit 170 receives the FFT interval, the maximum delay time, and the 1 OFDM symbol length Ns acquired by the setting information acquisition unit 160. The setting state balance determination unit 170 compares the setting state balance between the wireless terminal device 100 on the transmission side and the reception side by comparing the 1 OFDM symbol length Ns with the selected section (Nc−2M−Δ). . When 1 OFDM symbol length Ns> selection interval (Nc−2M−Δ), the setting state balance determination unit 170 determines that the setting state is not balanced, and the feedback information used for changing the setting on the transmission side The generation command signal is output to the feedback information generation unit 180.

  When receiving the generation command signal from the setting state balance determination unit 170, the feedback information generation unit 180 generates feedback information including the reception FFT interval Nc, the maximum delay time Δ, and the impulse response spread M.

  The transmission radio processing unit 190 transmits the feedback information generated by the feedback information generation unit 180 via the antenna after performing the radio transmission processing.

  As shown in FIG. 6, base station apparatus 200 of Embodiment 1 includes reception radio processing section 210, setting section 220, transmission signal generation section 230, modulation section 240, multicarrier modulation section 250, and transmission radio. And a processing unit 260.

  The reception wireless processing unit 210 receives a signal transmitted from the wireless terminal device 100 that is a communication partner via an antenna, and performs predetermined wireless reception processing (down-conversion, A / D conversion, etc.) on the received signal. Apply. The signal after the wireless processing is output to the setting unit 220.

  The setting unit 220 has an imbalance in the setting state when the feedback information generated by the feedback information generation unit 180 of the wireless terminal device 100 is included in the signal after wireless processing from the reception wireless processing unit 210. The symbol data size is changed to eliminate the imbalance. Specifically, the setting unit 220 receives the reception FFT interval Nc, the maximum delay time Δ, and the impulse response spread M included in the feedback information, and sets the condition of 1 OFDM symbol length Ns ≦ selection interval (Nc−2M−Δ). One OFDM symbol length Ns is changed so as to satisfy. Further, the setting unit 220 calculates the sampling rate Ns / Nc using the changed Ns. Then, setting unit 220 sets the changed Ns in multicarrier modulation unit 250 and sets the calculated sampling rate in transmission signal generation unit 230. In this way, it is possible to prevent a decrease in BER that occurs in the receiving-side wireless terminal device 100 due to an imbalance in the setting state.

  The transmission signal generation unit 230 generates transmission data by performing sampling according to the sampling rate set by the setting unit 220.

  Modulation section 240 modulates the transmission data generated by transmission signal generation section 230 and outputs the modulated signal to multicarrier modulation section 250.

  Multicarrier modulation section 250 adjusts the number of subcarriers to which the modulated signal is mapped according to the symbol data size set by setting section 220. Then, multicarrier modulation section 250 maps the modulation signal to subcarriers of the adjusted number of subcarriers, and then converts from the frequency direction to the time direction to form a multicarrier signal (here, an OFDM signal). This multicarrier signal is output to transmission radio processing section 260.

  Specifically, the multicarrier modulation unit 250 includes an S / P conversion unit 252, a subcarrier mapping unit 254, and an IFFT unit 256 as shown in FIG.

  The S / P conversion unit 252 adjusts the number of parallel data sequences (hereinafter sometimes referred to as “division number”) formed from one serial data sequence according to the symbol data size set by the setting unit 220. . The S / P converter 252 converts the modulated transmission data sequence into a parallel sequence corresponding to the adjusted number of divisions.

  The subcarrier mapping unit 254 forms a parallel signal by mapping each parallel sequence formed by the S / P conversion unit 252 to a corresponding subcarrier.

  The IFFT unit 256 forms a multicarrier signal (here, an OFDM signal) by converting the parallel signal from the subcarrier mapping unit 254 from the frequency direction to the time direction.

  Transmission radio processing section 260 transmits the multicarrier signal formed by IFFT section 256 via the antenna after performing radio transmission processing.

  Next, an operation in a wireless communication system including the wireless terminal device 100 and the base station device 200 having the above configuration will be described.

  When downlink data transmission is performed from the base station apparatus 200 to the radio terminal apparatus 100, the setting unit 120 in the radio terminal apparatus 100 uses the maximum delay amount of the delay wave specified using the delay profile and the impulse response of the FDE. Based on the spread, an FFT interval of Nc = Ns + 2M + Δ samples and an Ns symbol selection interval are set for the ISI removal processing unit 130. Then, when the FFT unit 132 and the selection unit 138 perform predetermined processing based on these setting values, the wireless terminal device 100 can obtain received data.

  Here, in order for radio terminal apparatus 100 to accurately demodulate and obtain received data, the selection section selected by selection section 138 needs to be at least one symbol length of the transmission signal formed on the transmission side. There is. That is, it is necessary to satisfy the condition of Ns ≦ (Nc−2M−Δ).

  However, depending on the characteristics of the wireless communication system and the setting states of the wireless terminal device 100 and the base station device 200, it may be possible that only the receiving wireless terminal device 100 cannot satisfy the above condition. Depending on the wireless communication system, there may be a case where the wireless terminal device 100 and the base station device 200 are in a mixed state with various communication capabilities (spec, remaining battery level, allowable service).

  As a first example, while the wireless terminal devices 100 having reception limits of 5 MHz, 10 MHz, and 20 MHz are mixed, the base station device 200 has a capability of transmitting a transmission band of 20 MHz, and each wireless terminal device A wireless communication system in which a bandwidth is allocated to 100 is conceivable. In this case, even if base station apparatus 200 transmits a signal with a symbol length corresponding to 20 MHz transmission, radio terminal apparatus 100 having only 5 MHz and 10 MHz reception capability cannot receive the transmission signal. That is, in this case, a relationship of Ns> (Nc−2M−Δ) is established, and an imbalance of the setting state is generated between the transmission side and the reception side.

  As a second example, the wireless terminal device 100 changes the reception bandwidth in accordance with the remaining battery level. That is, even when the transmission side and the reception side are balanced, it is conceivable that an unbalance occurs in the allowable communication capability set in the wireless terminal device 100 on the reception side.

  That is, as shown in FIG. 8, when Ns ≦ (Nc−2M−Δ) is satisfied, the radio terminal apparatus 100 on the receiving side can receive the transmission signal from the base station apparatus 200 with high accuracy. However, in the case of the above example, Ns> (Nc−2M−Δ) as shown in FIG. In this case, it is conceivable that the radio terminal apparatus 100 expands the reception FFT section and the selection section. However, if the reception FFT section and the selection section are the limits allowed for the radio terminal apparatus 100, it is not permitted.

  Therefore, in the present embodiment, when the setting state between the transmission side and the reception side is unbalanced, feedback information to the transmission side is transmitted. Specifically, the setting state balance determination unit 170 determines the balance of the setting state using the reception FFT interval, the selection interval, and the maximum delay time collected by the setting information acquisition unit 160. If the determination result indicates that the state is an unbalanced state, the feedback information generation unit 180 generates feedback information including the reception FFT interval Nc, the maximum delay time Δ, and the impulse response spread M, and transmits the generated feedback information to the transmission side. To do.

  In base station apparatus 200 on the transmission side, setting unit 220 changes the symbol data size in order to eliminate the imbalance. Specifically, the setting unit 220 receives the reception FFT interval Nc, the maximum delay time Δ, and the impulse response spread M included in the feedback information, and sets the condition of 1 OFDM symbol length Ns ≦ selection interval (Nc−2M−Δ). One OFDM symbol length Ns is changed so as to satisfy. Further, the setting unit 220 calculates the sampling rate Ns / Nc using the changed Ns. Then, setting unit 220 sets the changed Ns in multicarrier modulation unit 250 and sets the calculated sampling rate in transmission signal generation unit 230.

  By doing so, as shown in FIG. 10, 1 OFDM symbol length Ns ≦ selected section (Nc−2M−Δ) is satisfied, so that the setting state on the transmitting side and the receiving side is balanced. In this way, it is possible to prevent a decrease in BER that occurs in the receiving-side wireless terminal device 100 due to an imbalance in the setting state.

  As described above, according to the present embodiment, the received OFDM signal is subjected to Fourier transform in the receive Fourier transform section to be converted into a frequency domain signal, and then subjected to frequency domain equalization, and further subjected to inverse Fourier transform. A setting state balance determination unit 170 that determines the balance between the symbol length of the received OFDM signal and the selected section, to the wireless terminal device 100 as an OFDM receiving apparatus that extracts a part of the obtained time domain signal as a selected section to be demodulated, When the selection interval is shorter than the symbol length, feedback for generating feedback information to the transmission side including a reception Fourier transform interval, a maximum delay time of the received OFDM signal, and a spread of an impulse response in the frequency domain equalization process An information generation unit 180 is provided.

  By doing so, even if the reception FFT interval and the selection interval set in the radio terminal device 100 on the receiving side are the limits allowed for the radio terminal device 100, the reception FFT interval Nc, the maximum delay time Δ, and the impulse Feedback information including the response spread M is transmitted to the transmission side, and the transmission side can adjust the symbol length using this feedback information. Therefore, the radio terminal apparatus 100 on the reception side causes the setting state imbalance. It is possible to prevent a decrease in BER that occurs.

  Further, according to the present embodiment, the time obtained by performing frequency domain equalization after the received OFDM signal is Fourier-transformed in the received FFT interval and then being converted into a frequency-domain signal, and further subjected to inverse Fourier transform. A base station apparatus 200 as an OFDM transmission apparatus that transmits an OFDM signal toward an OFDM reception apparatus that extracts a part of the area signal as a selection section to be demodulated, and a reception FFT section, a maximum delay time of the received OFDM signal, and a frequency domain Using reception radio processing section 210 as an acquisition means for acquiring feedback information including a spread of an impulse response in equalization processing, and using the feedback information, the symbol length of the OFDM signal is equal to or shorter than the length of the selected section. In addition, as an adjustment means for adjusting the number of subcarriers to which modulation data is mapped A tough 220, was the arranged.

  By doing so, even if the reception FFT interval and the selection interval set in the radio terminal device 100 on the receiving side are the limits allowed for the radio terminal device 100, the reception FFT interval Nc, the maximum delay time Δ, and the impulse Feedback information including the response spread M is transmitted to the transmission side, and the transmission side can adjust the symbol length using this feedback information. Therefore, the radio terminal apparatus 100 on the reception side causes the setting state imbalance. It is possible to prevent a decrease in BER that occurs.

  Furthermore, the base station apparatus 200 modulates the transmission data, an S / P conversion unit 252 that forms a plurality of parallel data by serial-parallel conversion of the modulated signal, and inverse Fourier transforms the plurality of parallel data. An IFFT unit 256 for forming an OFDM signal, and the setting unit 220 sets the number of the parallel data formed in the S / P conversion unit 252 and the sampling rate of the transmission data in the transmission signal generation unit 230 The number of subcarriers is adjusted by changing.

(Embodiment 2)
In Embodiment 2, a case where SC-FDMA (Single-Carrier Frequency Division Multiple Access) is applied as a communication method will be described. The radio terminal apparatus on the receiving side is basically the same as radio terminal apparatus 100 of the first embodiment, but only P / S conversion section 146 used in multicarrier demodulation section 140 is replaced with an IFFT section. That is, the FFT unit 142 converts the signal sequence from the time direction to the frequency direction, the subcarrier demapping unit 144 performs demapping, the IFFT unit converts from the frequency direction to the time direction, and the obtained signal sequence is demodulated. 150. The demapping is performed with a mapping pattern corresponding to a subcarrier mapping unit 354 described later. There may be a case where mapping is not performed.

  As shown in FIG. 11, base station apparatus 300 of Embodiment 2 has multicarrier modulation section 350.

  Multicarrier modulation section 350 adjusts the number of subcarriers to which the modulated signal is mapped according to the symbol data size set by setting section 220. Then, multicarrier modulation section 350 maps the modulated signal to subcarriers of the adjusted number of subcarriers, and then converts from the frequency direction to the time direction to form a multicarrier signal (here, an OFDM signal). This multicarrier signal is output to transmission radio processing section 260.

  Specifically, the multicarrier modulation unit 350 includes an FFT unit 352, a subcarrier mapping unit 354, and an IFFT unit 356 as shown in FIG.

  The FFT unit 352 performs an FFT process on the data modulated by the modulation unit 240. By this processing, data is converted from a time domain signal to a frequency domain signal. The FFT unit 352 adjusts the number of components formed from one symbol (hereinafter sometimes referred to as “division number”) according to the symbol data size set by the setting unit 220. The data converted into the frequency domain is composed of K components respectively corresponding to K (corresponding to the number of divisions) frequencies.

  In subcarrier mapping section 354, each component of the data formed in FFT section 352 is output as it is as a signal assigned to the corresponding subcarrier.

  IFFT section 356 performs IFFT processing on the signal output from subcarrier mapping section 354. By this processing, the data is inversely converted from the frequency domain signal to the time domain signal.

  As described above, according to the present embodiment, the base station apparatus 300 as the OFDM transmission apparatus includes the modulation unit 240 that modulates transmission data, and the FFT unit 352 that Fourier-transforms the modulation signal to form a plurality of frequency components. A subcarrier mapping unit 354 that maps the plurality of frequency components to different subcarriers, and an IFFT unit 356 that forms an OFDM signal by performing inverse Fourier transform on the mapped frequency components. Unit 220 adjusts the number of subcarriers by changing the number of frequency components formed in FFT unit 352 and the sampling rate of transmission data in transmission signal generation unit 230.

(Other embodiments)
In the first and second embodiments, the frequency domain signal may be converted from the time domain signal to the frequency domain signal by using other frequency transform methods such as DFT and discrete Fourier transform in addition to FFT. . In addition to IFFT, other time conversion methods such as IDFT and discrete inverse Fourier transform may be used for conversion from frequency domain signals to time domain signals. In addition, the FFT interval may be represented as an FFT window. In addition, DFT of a circular convolution results in a simple product, the so-called convolution theorem is used to replace a time domain signal convolution operation with a frequency domain signal product, or a time domain signal product with a frequency domain signal convolution. Also good. Thereby, it is good also as a structure which considered the alternative of said signal conversion process.

  Further, the present invention is not limited to MMSE-FDE but can be similarly applied to other FDEs such as ZF-FDE. The present invention can be similarly applied to other digital transmission schemes using FDE (for example, MC-CDMA, DS-CDMA, IFDMA, Wavelet-OFDM, etc.).

  In the first embodiment and the second embodiment, the case where it is configured by hardware has been described as an example, but it may be realized by software.

  Each functional block used in the first embodiment and the second embodiment can be realized as an LSI that is typically an integrated circuit. This may be made into one chip, or may be made into one chip so as to include a part or all of it. The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration. Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. An FPGA that can be programmed after manufacturing the LSI or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used. Further, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. Biotechnology can be applied.

  Also, in the first and second embodiments, by carrying out so-called precoding in which a transmitting / receiving side possesses a table or a code book or the like classified by a selection section having a preset range and feeds back only the corresponding range number. It is also possible to reduce the amount of feedback information.

  The OFDM transmission apparatus and OFDM reception apparatus of the present invention maintain transmission efficiency while maintaining good BER characteristics even in a wireless communication system in which communication is performed between a plurality of wireless communication apparatuses having various communication capabilities. It is useful as something that can be enhanced.

  The present invention relates to an OFDM transmitter and an OFDM receiver.

  In recent years, wireless transmission schemes suitable for high-speed packet transmission have been studied. For this high-speed packet transmission, it is necessary to widen the use frequency band. It is known that when broadband transmission is performed by mobile communication, the communication channel becomes a frequency selective channel composed of a plurality of paths having different delay times. Therefore, in wideband transmission in mobile communication, as shown in FIG. 1, intersymbol interference (ISI: Inter Symbol Interference) in which the preceding symbol interferes with the subsequent symbol occurs. When this intersymbol interference occurs, the bit error rate (BER) characteristics deteriorate. Further, since the frequency selective channel is a channel whose channel transfer function varies within the frequency band, the spectrum of the signal received through such a channel is distorted.

  As a technique for improving the BER by removing the influence of ISI, there is frequency domain equalization (FDE) (for example, see Non-Patent Document 1). In FDE, a received signal block is decomposed into orthogonal frequency components by Fast Fourier Transform (FFT), and each frequency component is multiplied by an equalization weight approximated to the inverse of the channel transfer function, and then inverse Fast Fourier Transform is performed. (IFFT: Inverse Fast Fourier Transform) to convert to a time domain signal. This FDE can compensate for the distortion of the spectrum of the received signal. As a result, ISI is reduced and BER characteristics are improved. As the equalization weight, a minimum mean square error (MMSE) weight that minimizes the mean square error between the equalized frequency component and transmission signal component gives the best BER characteristics.

  However, in the technique described in Non-Patent Document 1, it is necessary that the received signal can be handled as a repeated signal having an FFT block length. Here, a signal that can be expressed by combining various waveforms that can be expressed in an arbitrary n period with a basic waveform having a block length of one period is referred to as a repetitive signal. For this reason, a guard interval (GI) that adds the same signal as the tail part of the symbol block to the head of the symbol block is provided on the transmission side. However, when the GI is provided, the data transmission rate is lowered by the GI length.

Thus, there is a wireless communication device disclosed in Patent Document 1 that can improve transmission efficiency while maintaining good BER characteristics. This wireless communication apparatus includes an FFT unit 14 that performs FFT on a received signal that does not have a GI to obtain a plurality of frequency components, an FDE unit 15 that performs frequency equalization on the obtained frequency components, and a frequency domain An IFFT unit 16 that obtains a signal sequence by performing IFFT on the equalized frequency components, a selection unit 17 that selects a part of the obtained signal sequence, and an FFT unit 14 and a selection unit, respectively, A setting unit 13 to be set in the unit 17, an FFT unit 21 for performing FFT on the selected signal sequence to obtain a plurality of frequency components, a P / S unit 22 for converting the obtained frequency components into a serial sequence, And a demodulator 18 that demodulates the frequency component converted into the serial sequence. With this configuration, it is possible to increase transmission efficiency while maintaining good BER characteristics.
JP 2006-304192 A D. Falconer, SL Ariyavistakul, A. Benyamin-Seeyar, and B. Eidson, “Frequency domain equalization for single-carrier broadband wireless systems”, IEEE Commun. Mag., Vol. 40, pp.58-66, Apr. 2002 .

  By the way, there is a wireless communication system in which communication is performed between a wireless terminal having various capabilities (spec, battery remaining amount, allowable service) and a base station. When the conventional wireless communication apparatus is applied to such a wireless communication system, there is a possibility that the BER characteristic cannot be maintained. That is, in order for the above-described conventional wireless communication apparatus to be effective, the condition that the selected section is 1 OFDM symbol length or longer must be satisfied, but the wireless communication system may not be able to satisfy the condition. . As a result, there is a problem that the transmission efficiency is also lowered due to the lowered BER characteristics.

  An object of the present invention is to provide an OFDM transmission capable of improving transmission efficiency while maintaining good BER characteristics even in a wireless communication system in which communication is performed between a plurality of wireless communication devices in various communication capabilities. An apparatus and an OFDM receiver are provided.

  The OFDM receiving apparatus of the present invention is a time domain obtained by performing frequency domain equalization processing after the received OFDM signal is Fourier transformed in the Fourier transform section to be converted to a frequency domain signal, and further inverse Fourier transformed. An OFDM receiver for extracting a part of a signal as a selection section to be demodulated, wherein the balance determination means for determining the balance between the symbol length of the received OFDM signal and the selection section, and the selection section is shorter than the symbol length And a feedback information generating means for generating feedback information to the transmitting side including a Fourier transform section, a maximum delay time of the received OFDM signal, and a spread of an impulse response in the frequency domain equalization process.

  The OFDM transmission apparatus of the present invention is a time domain obtained by performing frequency domain equalization after the received OFDM signal is Fourier transformed in the Fourier transform section to be converted to a frequency domain signal, and further inverse Fourier transformed. An OFDM transmitter that transmits an OFDM signal toward an OFDM receiver that extracts a part of the signal as a selection section to be demodulated, and includes an impulse in a Fourier transform section, a maximum delay time of the received OFDM signal, and a frequency domain equalization process An acquisition means for acquiring feedback information including a response spread; and using the feedback information, the number of subcarriers to which modulation data is mapped so that a symbol length of the OFDM signal is equal to or less than a length of the selection interval And an adjusting means for adjusting.

  According to the present invention, OFDM transmission capable of improving transmission efficiency while maintaining good BER characteristics even in a wireless communication system in which communication is performed between a plurality of wireless communication devices in various communication capabilities. An apparatus and an OFDM receiver can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the embodiments, the same components are denoted by the same reference numerals, and the description thereof will be omitted because it is redundant.

(Embodiment 1)
First, the principle of the basic operation of the FDE according to this embodiment will be described.

  As described in Patent Document 1, in this FDE, when the block length of each symbol block is Nc symbols, Nc equalization weights w (k) (k = 0 to Nc−1) are set. Use. That is, FDE is equivalent to linear filter processing with a transfer function w (k) (k = 0 to Nc−1). The impulse response of the FDE is concentrated in a narrow range around the time t = 0.

  Further, the FDE according to the present embodiment does not require a GI. For this reason, when a plurality of paths having different delays are present in the propagation path, ISI from the tail part of the previous symbol block occurs at the head part of each symbol block. For example, if the maximum value of the delay time difference between the L paths (the maximum delay amount of the delayed wave) is Δ symbols, the ISI interval is the Δ symbol interval from the beginning of the symbol block. As described above, when the ISI in the Δ symbol section is generated at the head of the symbol block, a correct frequency component cannot be obtained in the FFT, so that the signal sequence after FDE is distorted. The distortion due to the ISI spreads in time by the extent of the impulse response. In other words, the distortion due to the ISI is so small that it can be ignored at a position distant in time from the ISI interval.

  Therefore, for example, if the spread of the impulse response is ± M symbols, the distortion due to ISI is as shown in FIG. 2, and the distortion in the t = Δ + M to Nc−M−1 symbol section is ignored in each symbol block after FDE. It becomes small as much as possible. Therefore, as shown in FIG. 3, if only the signal in the t = Δ + M to Nc−M−1 symbol section is selected in each symbol block after FDE, the distortion can be reduced without adding GI to each symbol block. A signal after no equalization can be obtained. In addition, in order to obtain a continuous equalized signal, the starting point of the FFT interval is sequentially shifted by Nc-2M-Δ symbols. In this way, a plurality of FFT sections are set to overlap each other, and a selection section shorter than each FFT section is set, so that a continuous signal without distortion can be obtained in FDE for a signal having no GI. Obtainable. In this way, FDE that does not require GI becomes possible. As a result, it is not necessary to add a GI on the transmission side, so that transmission efficiency can be improved.

  Next, a configuration of main parts of the wireless terminal device in the wireless communication system according to the present embodiment will be described.

  As shown in FIG. 4, radio terminal apparatus 100 according to Embodiment 1 includes reception radio processing section 110, setting section 120, ISI removal processing section 130, multicarrier demodulation section 140, demodulation section 150, and setting information. An acquisition unit 160, a setting state balance determination unit 170, a feedback information generation unit 180, and a transmission wireless processing unit 190 are included.

Reception radio processing section 110 receives a multicarrier signal transmitted from a communication partner via an antenna, and performs predetermined radio reception processing (down-conversion, A / D conversion, etc.) on the received signal. The multi-carrier signal here is an OFDM signal having no GI. The signal after radio processing (reception sequence signal) is output to setting section 120 and ISI removal processing section 130.

  The setting unit 120 outputs timing information (symbol timing) obtained by performing synchronization processing using the signal after radio processing to the ISI removal processing unit 130. Further, the setting unit 120 performs an FFT interval of Nc = Ns + 2M + Δ samples to the ISI removal processing unit 130 based on the maximum delay amount of the delay wave specified using the delay profile and the spread of the impulse response of the FDE. And a selection section of the Ns symbol. Further, as illustrated in FIG. 3, the setting unit 120 sets the start point of the FFT interval and the selection interval to be set this time from the start point of the FFT interval and the selection interval set last time, by Nc−2M−Δ. Set to a timing shifted by a symbol. Here, it is assumed that the maximum delay amount of the delayed wave is Δ symbol and the spread of the impulse response of FDE is ± M symbol. Ns corresponds to the symbol length of the transmission signal that is normally transmitted by the communication partner.

  The ISI cancellation processing unit 130 performs ISI cancellation processing on the signal after the radio reception processing, and outputs the signal after ISI cancellation processing to the multicarrier demodulation unit 140.

  The ISI removal processing unit 130 includes an FFT unit 132, an FDE unit 134, an IFFT unit 136, and a selection unit 138.

  As shown in FIG. 3, the FFT unit 132 performs FFT of a size of Nc = Ns + 2M + Δ on the received signal sequence having no GI in the FFT interval set by the setting unit 120 to obtain a plurality of frequency components. The reception FFT section of the FFT unit 132 is Nc.

  The FDE unit 134 performs FDE on each frequency component by multiplying each frequency component by the MMSE equalization weight. Each frequency component after the FDE is output to the IFFT unit 136 in parallel. As the MMSE equalization weight, for example, “Takeda et al.,“ The transmission performance with space and frequency-domain process for DS-CDMA. ) ", Technical report of IEICE Technical Report, RCS2003-33, pp.21-25, 2003-05" is used.

  IFFT section 136 performs IFFT on each frequency component after FDE to obtain a signal sequence after FDE.

  The selection unit 138 selects a part of the Nc symbol signal sequence, that is, a signal sequence in the selection section set by the setting unit 120, and outputs the selected signal sequence to the multicarrier demodulation unit 140.

  As shown in FIG. 5, multicarrier demodulation section 140 includes FFT section 142, subcarrier demapping section 144, and P / S conversion section 146. The FFT unit 142 converts the signal sequence from the selection unit 138 from a time direction signal to a frequency direction signal. The subcarrier demapping unit 144 performs demapping of the signal in the frequency direction obtained by the FFT unit 142. The demapping is performed with a mapping pattern corresponding to a subcarrier mapping unit 254 described later. There may be a case where mapping is not performed. The parallel signal is output to the P / S converter 146. P / S conversion section 146 converts the parallel signal from subcarrier demapping section 144 into a serial signal, and outputs the obtained signal sequence to demodulation section 150.

  Demodulation section 150 performs demodulation processing on the signal sequence from multicarrier demodulation section 140 to obtain received data.

  The setting information acquisition unit 160 acquires the reception FFT interval and the selection interval, the maximum delay time, and the spread of the impulse response set by the setting unit 120 in the ISI removal processing unit 130 from the setting unit 120, and sets the broadcast channel of the reception signal. The included OFDM symbol length Ns on the transmission side is acquired.

  The setting state balance determination unit 170 receives the FFT interval, the maximum delay time, and the 1 OFDM symbol length Ns acquired by the setting information acquisition unit 160. The setting state balance determination unit 170 compares the setting state balance between the wireless terminal device 100 on the transmission side and the reception side by comparing the 1 OFDM symbol length Ns with the selected section (Nc−2M−Δ). . When 1 OFDM symbol length Ns> selection interval (Nc−2M−Δ), the setting state balance determination unit 170 determines that the setting state is not balanced, and the feedback information used for setting change on the transmission side The generation command signal is output to the feedback information generation unit 180.

  When receiving the generation command signal from the setting state balance determination unit 170, the feedback information generation unit 180 generates feedback information including the reception FFT interval Nc, the maximum delay time Δ, and the impulse response spread M.

  The transmission radio processing unit 190 transmits the feedback information generated by the feedback information generation unit 180 via the antenna after performing the radio transmission processing.

  As shown in FIG. 6, base station apparatus 200 of Embodiment 1 includes reception radio processing section 210, setting section 220, transmission signal generation section 230, modulation section 240, multicarrier modulation section 250, and transmission radio. And a processing unit 260.

  The reception wireless processing unit 210 receives a signal transmitted from the wireless terminal device 100 that is a communication partner via an antenna, and performs predetermined wireless reception processing (down-conversion, A / D conversion, etc.) on the received signal. Apply. The signal after the wireless processing is output to the setting unit 220.

  The setting unit 220 has an imbalance in the setting state when the feedback information generated by the feedback information generation unit 180 of the wireless terminal device 100 is included in the signal after wireless processing from the reception wireless processing unit 210. The symbol data size is changed to eliminate the imbalance. Specifically, the setting unit 220 receives the reception FFT interval Nc, the maximum delay time Δ, and the impulse response spread M included in the feedback information, and sets the condition of 1 OFDM symbol length Ns ≦ selection interval (Nc−2M−Δ). One OFDM symbol length Ns is changed so as to satisfy. Further, the setting unit 220 calculates the sampling rate Ns / Nc using the changed Ns. Then, setting unit 220 sets the changed Ns in multicarrier modulation unit 250 and sets the calculated sampling rate in transmission signal generation unit 230. In this way, it is possible to prevent a decrease in BER that occurs in the receiving-side wireless terminal device 100 due to an imbalance in the setting state.

  The transmission signal generation unit 230 generates transmission data by performing sampling according to the sampling rate set by the setting unit 220.

  Modulation section 240 modulates the transmission data generated by transmission signal generation section 230 and outputs the modulated signal to multicarrier modulation section 250.

Multicarrier modulation section 250 adjusts the number of subcarriers to which the modulated signal is mapped according to the symbol data size set by setting section 220. Then, multicarrier modulation section 250 maps the modulation signal to subcarriers of the adjusted number of subcarriers, and then converts from the frequency direction to the time direction to form a multicarrier signal (here, an OFDM signal). This multicarrier signal is output to transmission radio processing section 260.

  Specifically, the multicarrier modulation unit 250 includes an S / P conversion unit 252, a subcarrier mapping unit 254, and an IFFT unit 256 as shown in FIG.

  The S / P conversion unit 252 adjusts the number of parallel data sequences (hereinafter sometimes referred to as “division number”) formed from one serial data sequence according to the symbol data size set by the setting unit 220. . The S / P converter 252 converts the modulated transmission data sequence into a parallel sequence corresponding to the adjusted number of divisions.

  The subcarrier mapping unit 254 forms a parallel signal by mapping each parallel sequence formed by the S / P conversion unit 252 to a corresponding subcarrier.

  The IFFT unit 256 forms a multicarrier signal (here, an OFDM signal) by converting the parallel signal from the subcarrier mapping unit 254 from the frequency direction to the time direction.

  Transmission radio processing section 260 transmits the multicarrier signal formed by IFFT section 256 via the antenna after performing radio transmission processing.

  Next, an operation in a wireless communication system including the wireless terminal device 100 and the base station device 200 having the above configuration will be described.

  When downlink data transmission is performed from the base station apparatus 200 to the radio terminal apparatus 100, the setting unit 120 in the radio terminal apparatus 100 uses the maximum delay amount of the delay wave specified using the delay profile and the impulse response of the FDE. Based on the spread, an FFT interval of Nc = Ns + 2M + Δ samples and an Ns symbol selection interval are set for the ISI removal processing unit 130. Then, when the FFT unit 132 and the selection unit 138 perform predetermined processing based on these setting values, the wireless terminal device 100 can obtain received data.

  Here, in order for radio terminal apparatus 100 to accurately demodulate and obtain received data, the selection section selected by selection section 138 needs to be at least one symbol length of the transmission signal formed on the transmission side. There is. That is, it is necessary to satisfy the condition of Ns ≦ (Nc−2M−Δ).

  However, depending on the characteristics of the wireless communication system and the setting states of the wireless terminal device 100 and the base station device 200, it may be possible that only the receiving wireless terminal device 100 cannot satisfy the above condition. Depending on the wireless communication system, there may be a case where the wireless terminal device 100 and the base station device 200 are in a mixed state with various communication capabilities (spec, remaining battery level, allowable service).

  As a first example, while the wireless terminal devices 100 having reception limits of 5 MHz, 10 MHz, and 20 MHz are mixed, the base station device 200 has a capability of transmitting a transmission band of 20 MHz, and each wireless terminal device A wireless communication system in which a bandwidth is allocated to 100 is conceivable. In this case, even if base station apparatus 200 transmits a signal with a symbol length corresponding to 20 MHz transmission, radio terminal apparatus 100 having only 5 MHz and 10 MHz reception capability cannot receive the transmission signal. That is, in this case, a relationship of Ns> (Nc−2M−Δ) is established, and an imbalance of the setting state is generated between the transmission side and the reception side.

  As a second example, the wireless terminal device 100 changes the reception bandwidth in accordance with the remaining battery level. That is, even when the transmission side and the reception side are balanced, it is conceivable that an unbalance occurs in the allowable communication capability set in the wireless terminal device 100 on the reception side.

  That is, as shown in FIG. 8, when Ns ≦ (Nc−2M−Δ) is satisfied, the radio terminal apparatus 100 on the receiving side can receive the transmission signal from the base station apparatus 200 with high accuracy. However, in the case of the above example, Ns> (Nc−2M−Δ) as shown in FIG. In this case, it is conceivable that the radio terminal apparatus 100 expands the reception FFT section and the selection section. However, if the reception FFT section and the selection section are the limits allowed for the radio terminal apparatus 100, it is not permitted.

  Therefore, in the present embodiment, when the setting state between the transmission side and the reception side is unbalanced, feedback information to the transmission side is transmitted. Specifically, the setting state balance determination unit 170 determines the balance of the setting state using the reception FFT interval, the selection interval, and the maximum delay time collected by the setting information acquisition unit 160. If the determination result indicates that the state is an unbalanced state, the feedback information generation unit 180 generates feedback information including the reception FFT interval Nc, the maximum delay time Δ, and the impulse response spread M, and transmits the generated feedback information to the transmission side. To do.

  In base station apparatus 200 on the transmission side, setting unit 220 changes the symbol data size in order to eliminate the imbalance. Specifically, the setting unit 220 receives the reception FFT interval Nc, the maximum delay time Δ, and the impulse response spread M included in the feedback information, and sets the condition of 1 OFDM symbol length Ns ≦ selection interval (Nc−2M−Δ). One OFDM symbol length Ns is changed so as to satisfy. Further, the setting unit 220 calculates the sampling rate Ns / Nc using the changed Ns. Then, setting unit 220 sets the changed Ns in multicarrier modulation unit 250 and sets the calculated sampling rate in transmission signal generation unit 230.

  By doing so, as shown in FIG. 10, 1 OFDM symbol length Ns ≦ selected section (Nc−2M−Δ) is satisfied, so that the setting state on the transmitting side and the receiving side is balanced. In this way, it is possible to prevent a decrease in BER that occurs in the receiving-side wireless terminal device 100 due to an imbalance in the setting state.

  As described above, according to the present embodiment, the received OFDM signal is subjected to Fourier transform in the receive Fourier transform section to be converted into a frequency domain signal, and then subjected to frequency domain equalization, and further subjected to inverse Fourier transform. A setting state balance determination unit 170 that determines the balance between the symbol length of the received OFDM signal and the selected section, to the wireless terminal device 100 as an OFDM receiving apparatus that extracts a part of the obtained time domain signal as a selected section to be demodulated, When the selection interval is shorter than the symbol length, feedback for generating feedback information to the transmission side including a reception Fourier transform interval, a maximum delay time of the received OFDM signal, and a spread of an impulse response in the frequency domain equalization process An information generation unit 180 is provided.

  By doing so, even if the reception FFT interval and the selection interval set in the radio terminal device 100 on the receiving side are the limits allowed for the radio terminal device 100, the reception FFT interval Nc, the maximum delay time Δ, and the impulse Feedback information including the response spread M is transmitted to the transmission side, and the transmission side can adjust the symbol length using this feedback information. Therefore, the radio terminal apparatus 100 on the reception side causes the setting state imbalance. It is possible to prevent a decrease in BER that occurs.

  Further, according to the present embodiment, the time obtained by performing frequency domain equalization after the received OFDM signal is Fourier-transformed in the received FFT interval and then being converted into a frequency-domain signal, and further subjected to inverse Fourier transform. A base station apparatus 200 as an OFDM transmission apparatus that transmits an OFDM signal toward an OFDM reception apparatus that extracts a part of the area signal as a selection section to be demodulated, and a reception FFT section, a maximum delay time of the received OFDM signal, and a frequency domain Using reception radio processing section 210 as an acquisition means for acquiring feedback information including a spread of an impulse response in equalization processing, and using the feedback information, the symbol length of the OFDM signal is equal to or shorter than the length of the selected section. In addition, as an adjustment means for adjusting the number of subcarriers to which modulation data is mapped A tough 220, was the arranged.

  By doing so, even if the reception FFT interval and the selection interval set in the radio terminal device 100 on the receiving side are the limits allowed for the radio terminal device 100, the reception FFT interval Nc, the maximum delay time Δ, and the impulse Feedback information including the response spread M is transmitted to the transmission side, and the transmission side can adjust the symbol length using this feedback information. Therefore, the radio terminal apparatus 100 on the reception side causes the setting state imbalance. It is possible to prevent a decrease in BER that occurs.

  Furthermore, the base station apparatus 200 modulates the transmission data, an S / P conversion unit 252 that forms a plurality of parallel data by serial-parallel conversion of the modulated signal, and inverse Fourier transforms the plurality of parallel data. An IFFT unit 256 for forming an OFDM signal, and the setting unit 220 sets the number of the parallel data formed in the S / P conversion unit 252 and the sampling rate of the transmission data in the transmission signal generation unit 230 The number of subcarriers is adjusted by changing.

(Embodiment 2)
In Embodiment 2, a case where SC-FDMA (Single-Carrier Frequency Division Multiple Access) is applied as a communication method will be described. The radio terminal apparatus on the receiving side is basically the same as radio terminal apparatus 100 of the first embodiment, but only P / S conversion section 146 used in multicarrier demodulation section 140 is replaced with an IFFT section. That is, the FFT unit 142 converts the signal sequence from the time direction to the frequency direction, the subcarrier demapping unit 144 performs demapping, the IFFT unit converts from the frequency direction to the time direction, and the obtained signal sequence is demodulated. 150. The demapping is performed with a mapping pattern corresponding to a subcarrier mapping unit 354 described later. There may be a case where mapping is not performed.

  As shown in FIG. 11, base station apparatus 300 of Embodiment 2 has multicarrier modulation section 350.

  Multicarrier modulation section 350 adjusts the number of subcarriers to which the modulated signal is mapped according to the symbol data size set by setting section 220. Then, multicarrier modulation section 350 maps the modulated signal to subcarriers of the adjusted number of subcarriers, and then converts from the frequency direction to the time direction to form a multicarrier signal (here, an OFDM signal). This multicarrier signal is output to transmission radio processing section 260.

  Specifically, the multicarrier modulation unit 350 includes an FFT unit 352, a subcarrier mapping unit 354, and an IFFT unit 356 as shown in FIG.

The FFT unit 352 performs an FFT process on the data modulated by the modulation unit 240. By this processing, data is converted from a time domain signal to a frequency domain signal. The FFT unit 352 adjusts the number of components formed from one symbol (hereinafter sometimes referred to as “division number”) according to the symbol data size set by the setting unit 220. The data converted into the frequency domain is composed of K components respectively corresponding to K (corresponding to the number of divisions) frequencies.

  In subcarrier mapping section 354, each component of the data formed in FFT section 352 is output as it is as a signal assigned to the corresponding subcarrier.

  IFFT section 356 performs IFFT processing on the signal output from subcarrier mapping section 354. By this processing, the data is inversely converted from the frequency domain signal to the time domain signal.

  As described above, according to the present embodiment, the base station apparatus 300 as the OFDM transmission apparatus includes the modulation unit 240 that modulates transmission data, and the FFT unit 352 that Fourier-transforms the modulation signal to form a plurality of frequency components. A subcarrier mapping unit 354 that maps the plurality of frequency components to different subcarriers, and an IFFT unit 356 that forms an OFDM signal by performing inverse Fourier transform on the mapped frequency components. Unit 220 adjusts the number of subcarriers by changing the number of frequency components formed in FFT unit 352 and the sampling rate of transmission data in transmission signal generation unit 230.

(Other embodiments)
In the first and second embodiments, the frequency domain signal may be converted from the time domain signal to the frequency domain signal by using other frequency transform methods such as DFT and discrete Fourier transform in addition to FFT. . In addition to IFFT, other time conversion methods such as IDFT and discrete inverse Fourier transform may be used for conversion from frequency domain signals to time domain signals. In addition, the FFT interval may be represented as an FFT window. In addition, DFT of a circular convolution results in a simple product, the so-called convolution theorem is used to replace a time domain signal convolution operation with a frequency domain signal product, or a time domain signal product with a frequency domain signal convolution. Also good. Thereby, it is good also as a structure which considered the alternative of said signal conversion process.

  Further, the present invention is not limited to MMSE-FDE but can be similarly applied to other FDEs such as ZF-FDE. The present invention can be similarly applied to other digital transmission schemes using FDE (for example, MC-CDMA, DS-CDMA, IFDMA, Wavelet-OFDM, etc.).

  In the first embodiment and the second embodiment, the case where it is configured by hardware has been described as an example, but it may be realized by software.

  Each functional block used in the first embodiment and the second embodiment can be realized as an LSI that is typically an integrated circuit. This may be made into one chip, or may be made into one chip so as to include a part or all of it. The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration. Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. An FPGA that can be programmed after manufacturing the LSI or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used. Further, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. Biotechnology can be applied.

  Also, in the first and second embodiments, by carrying out so-called precoding in which a transmitting / receiving side possesses a table or a code book or the like classified by a selection section having a preset range and feeds back only the corresponding range number. It is also possible to reduce the amount of feedback information.

  The OFDM transmission apparatus and OFDM reception apparatus of the present invention maintain transmission efficiency while maintaining good BER characteristics even in a wireless communication system in which communication is performed between a plurality of wireless communication apparatuses having various communication capabilities. It is useful as something that can be enhanced.

Illustration of ISI Diagram for explaining distortion by ISI Operation explanatory diagram of FDE according to the embodiment of the present invention 1 is a block diagram showing a configuration of a wireless terminal device according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a configuration of a wireless terminal apparatus according to Embodiment 1 FIG. 2 is a block diagram showing a configuration of a base station apparatus according to Embodiment 1 FIG. 2 is a block diagram showing a configuration of a base station apparatus according to Embodiment 1 The figure which uses for description of the relationship between the symbol length of a state in which the setting state is balanced and the reception FFT interval The figure which uses for description of the relationship between the symbol length of a state where the setting state is not balanced and the reception FFT interval The figure which shows the state after taking the setting state balance from the state of FIG. Block diagram showing a configuration of a base station apparatus according to Embodiment 2

Claims (4)

The received OFDM signal is transformed into a frequency domain signal by being Fourier transformed in the Fourier transform section, and then subjected to frequency domain equalization, and further a part of the time domain signal obtained by inverse Fourier transformation is demodulated. An OFDM receiver that extracts as a selected section,
Balance determination means for determining the balance between the symbol length of the received OFDM signal and the selected section;
When the selection interval is shorter than the symbol length, feedback information generation for generating feedback information to the transmission side including a Fourier transform interval, a maximum delay time of the received OFDM signal, and a spread of an impulse response in the frequency domain equalization process Means,
An OFDM receiver comprising: The received OFDM signal is transformed into a frequency domain signal by being Fourier transformed in the Fourier transform section, and then subjected to frequency domain equalization, and further a part of the time domain signal obtained by inverse Fourier transformation is demodulated. An OFDM transmitter that transmits an OFDM signal toward an OFDM receiver that is selected as a selection section,
An acquisition means for acquiring feedback information including a Fourier transform section, a maximum delay time of a received OFDM signal, and a spread of an impulse response in frequency domain equalization processing;
An adjustment unit that adjusts the number of subcarriers to which modulation data is mapped using the feedback information so that the symbol length of the OFDM signal is equal to or less than the length of the selection section;
An OFDM transmitter comprising: The OFDM transmitter includes a modulation unit that modulates transmission data, a serial-parallel conversion unit that performs serial-parallel conversion on the modulation signal to form a plurality of parallel data, and an OFDM signal obtained by performing an inverse Fourier transform on the plurality of parallel data. And an inverse Fourier transform means for forming
The adjustment means adjusts the number of subcarriers by changing the number of parallel data formed by the serial-parallel conversion means and a sampling rate of the transmission data.
The OFDM transmitter according to claim 2. The OFDM transmitter includes: modulation means for modulating transmission data; Fourier transform means for Fourier transforming a modulated signal to form a plurality of frequency components; mapping means for mapping the plurality of frequency components to different subcarriers; An inverse Fourier transform means for forming an OFDM signal by performing an inverse Fourier transform on the mapped frequency components,
The adjusting means adjusts the number of subcarriers by changing the number of the frequency components formed by the Fourier transform means and the sampling rate of the transmission data.
The OFDM transmitter according to claim 2.

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