WO2009131155A1 - 無線通信システム及びにそれに用いる送信装置 - Google Patents

無線通信システム及びにそれに用いる送信装置 Download PDF

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Publication number
WO2009131155A1
WO2009131155A1 PCT/JP2009/058009 JP2009058009W WO2009131155A1 WO 2009131155 A1 WO2009131155 A1 WO 2009131155A1 JP 2009058009 W JP2009058009 W JP 2009058009W WO 2009131155 A1 WO2009131155 A1 WO 2009131155A1
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Prior art keywords
frequency
signal
unit
transmission
assigned
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English (en)
French (fr)
Japanese (ja)
Inventor
藤　晋平
窪田　稔
泰弘 浜口
中村　理
一成 横枕
政一 三瓶
伸一 宮本
信介 衣斐
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Sharp Corp
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Sharp Corp
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Priority to US12/988,985 priority Critical patent/US8995540B2/en
Priority to CN200980114441.1A priority patent/CN102017485A/zh
Priority to EP09734509A priority patent/EP2271011A1/en
Publication of WO2009131155A1 publication Critical patent/WO2009131155A1/ja
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2626—Arrangements specific to the transmitter only
    • H04L27/2627—Modulators
    • H04L27/2634—Inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators in combination with other circuits for modulation
    • H04L27/2636—Inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators in combination with other circuits for modulation with FFT or DFT modulators, e.g. standard single-carrier frequency-division multiple access [SC-FDMA] transmitter or DFT spread orthogonal frequency division multiplexing [DFT-SOFDM]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0037—Inter-user or inter-terminal allocation
    • H04L5/0039—Frequency-contiguous, i.e. with no allocation of frequencies for one user or terminal between the frequencies allocated to another
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/56—Allocation or scheduling criteria for wireless resources based on priority criteria
    • H04W72/563—Allocation or scheduling criteria for wireless resources based on priority criteria of the wireless resources
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H04L25/03171—Arrangements involving maximum a posteriori probability [MAP] detection

Definitions

  • the present invention can accommodate more terminals in a limited band by setting the number of subcarriers constituting one subchannel smaller than the number of signals output in parallel from the DFT section of each terminal. And a wireless communication system capable of obtaining a higher transmission rate and a transmission device used therefor.
  • the E-UTRA Evolved Universal Terrestrial Radio Access
  • OFDMA Orthogonal Frequency
  • SC-FDMA Single Carrier-Frequency Division Multiple Access
  • the OFDMA scheme is a scheme in which a user accesses a resource block unit divided by time and frequency using an OFDM signal excellent in resistance to multipath fading, but has a high PAPR (Peak-to-Average Power Ratio). ) Because of its characteristics, it is not suitable as an uplink transmission method with severe transmission power limitation.
  • the SC-FDMA scheme is suitable for uplink transmission because PAPR characteristics can be kept low and a wide coverage can be ensured compared to a multicarrier scheme such as OFDM (Non-patent Document 1).
  • FIG. 10 shows the configuration of a terminal device when this SC-FDMA method is used for uplink transmission.
  • transmission section error correction encoding is performed in encoding section 1000, and modulation section 1001 performs modulation.
  • the modulated transmission signal is serial-parallel converted in an S / P (Serial-to-Parallel) conversion unit 1002 and then converted into a frequency-domain signal in a DFT (Discrete-Fourier-Transform) unit 1003.
  • the transmission signal thus converted into a frequency domain signal is assigned to a subcarrier used for transmission in subcarrier mapping section 1004.
  • the assignment at this time is performed based on mapping information transmitted from the base station apparatus, received by the receiving antenna unit 1011, demodulated by the receiving unit 1014 via the radio unit 1012, the A / D (Analog-to-Digital) converting unit 1013. In other words, zeros are inserted in subcarriers that are not used for transmission.
  • DFT section 1003 time-frequency conversion having the same size as the number of subcarriers constituting one subchannel determined by the system is performed, and all signals after time-frequency conversion are given subcarriers (subchannels). Assigned and transmitted.
  • FIG. 11 (a) shows a localized arrangement
  • FIG. 11 (b) shows a distributed arrangement
  • the number of subcarriers constituting one subchannel is 12, and 6 users are frequency division multiplexed. Yes.
  • the localized arrangement is suitable for obtaining multi-user diversity gain
  • the distributed arrangement is suitable for obtaining frequency diversity gain.
  • a transmission signal allocated on a subcarrier (subchannel) used for transmission in the subcarrier mapping unit 1004 of the terminal apparatus of FIG. 10 is then input to an IDFT (Inverse Discrete Fourier Transform) unit 1005, and the frequency domain Are converted to time domain signals.
  • IDFT Inverse Discrete Fourier Transform
  • a CP (Cyclic Prefix) inserting unit 1007 inserts a CP (a signal obtained by copying the symbol after IDFT) via a P / S (Parallel to Serial) converting unit 1006, and D / A (Digital to Analog).
  • the radio unit 1009 After being converted into an analog signal by the conversion unit 1008, the radio unit 1009 up-converts it to a radio frequency band signal and transmits it from the transmission antenna unit 1010.
  • the transmission signal generated in this way has a feature that the PAPR is lower than that of the multicarrier signal.
  • FIG. 12 shows the configuration of a base station apparatus that receives a signal transmitted from the terminal apparatus of FIG.
  • a base station apparatus that receives an SC-FDMA signal a signal received by an antenna unit 2000 is first converted to a frequency that can be A / D converted by a radio unit 2001, and then A The digital signal is converted by the / D converter 2002.
  • symbol synchronization is established in the synchronization unit 2003, and after the CP is removed for each symbol in the CP removal unit 2004, the time domain signal is transmitted to the frequency domain in the DFT unit 2006 via the S / P conversion unit 2005. Converted to a signal.
  • a pilot signal for propagation path estimation converted into a frequency domain signal (a known signal transmitted together with the data signal in the terminal device) is sent to the propagation path estimation unit 2007, and the propagation path is estimated.
  • the signal received by the base station apparatus is obtained by frequency-division multiplexing signals transmitted from a plurality of terminals, and mapping information determined in advance by the scheduling unit 2012 (which terminal apparatus is which Based on the information indicating whether or not subcarriers are used, the subcarrier demapping unit 2008 collects the used subcarriers (subcarriers constituting one subchannel) for each terminal device. Then, the equalization unit 2009 performs equalization processing on the reception subcarriers grouped for each terminal device using the propagation path estimation value, and the IDFT unit 2010 converts the frequency domain signal into the time domain signal. Thereafter, the demodulation / error correction decoding unit 2011 reproduces transmission data for each terminal device.
  • the reception level measurement pilot signal is sent from the DFT unit 2006 to the scheduling unit 2012. Based on the measurement result of the reception level using this signal, the scheduling unit 2012 performs scheduling in consideration of the propagation status of each terminal.
  • the mapping information determined in the scheduling unit 2012 is modulated in the transmission unit 2013, transmitted through the D / A unit 2014, the radio unit 2015, and the like, and then transmitted from the antenna unit 2016 to each terminal. This mapping information is used for transmission on the terminal side after the next frame.
  • the SC-FDMA scheme described above is the most promising candidate for the uplink transmission scheme of the E-UTRA system.
  • the SC-FDMA system like the OFDMA system, is a system that allows users to access resource blocks that are completely divided by time and frequency.
  • the PAPR characteristics are kept low and a wide coverage is secured.
  • a 1-cell reuse system can be realized.
  • the frequency resource strain is further accelerating as the number of users increases, there is a limit to the number of users that can be accommodated in the SC-FDMA system. It is necessary to construct a realized system.
  • the present invention intends to provide a radio communication system capable of accommodating a larger number of terminals in a limited band and capable of obtaining a higher transmission rate as a whole system, and a transmission device used therefor. Is.
  • a frequency-spread transmission signal is transmitted to any one of a plurality of frequency channels defined by a certain frequency band composed of a plurality of subcarriers and to a plurality of time channels defined by a certain time length.
  • a wireless communication system comprising: a transmission device that allocates and transmits; and a reception device that receives the transmission signal, The transmitter deletes a part of the frequency spread signal assigned to the frequency channel, reduces the number of subcarriers per frequency channel, converts the signal into a time domain signal, and transmits,
  • the receiving apparatus is characterized in that the received signal is converted into a frequency domain signal and separated into signals for each frequency channel, and nonlinear transmission equalization is performed to reproduce a transmission signal.
  • the transmitting apparatus deletes a signal corresponding to one or more subcarriers from one or both ends of the spread spectrum signal allocated to the frequency channel, and allocates the signal to the frequency channel. .
  • the transmission device is characterized in that the number of signals to be deleted is changed according to a frequency channel to which a frequency spread signal is assigned.
  • the transmission device is characterized in that the number of signals to be deleted is changed according to a time channel to which a frequency spread signal is assigned.
  • the transmission device is characterized in that the number of frequency spread signals allocated to the frequency channel and actually transmitted is the same among a plurality of transmission devices.
  • the receiving apparatus is characterized in that a zero is inserted into one or more subcarrier positions from one or both ends deleted in the transmitting apparatus, and nonlinear non-linear equalization processing is performed.
  • the present invention assigns a frequency-spread transmission signal to any one of a plurality of frequency channels defined by a certain frequency band composed of a plurality of subcarriers and to a plurality of time channels defined by a certain time length.
  • a transmitting device for transmitting Modulating means for modulating a transmission signal, frequency converting means for frequency-spreading the modulated signal to convert it to a frequency domain signal, and removing a part of the frequency spread signal assigned to the frequency channel, Clipping means for reducing the number of subcarriers per channel, mapping means for assigning frequency signals after clipping to frequency channels, Time conversion means for converting a frequency domain signal into a time domain signal and assigning it to a time channel.
  • the clipping means is characterized in that the number of signals to be deleted is changed according to a frequency channel to which a frequency spread signal is assigned.
  • the clipping means is characterized in that the number of signals to be deleted is changed according to a time channel to which a frequency spread signal is assigned.
  • mapping means is characterized in that the number of frequency spread signals allocated to the frequency channel and actually transmitted is the same in a plurality of transmission apparatuses.
  • part of the frequency spread signal assigned to the frequency channel is deleted, and the number of subcarriers per frequency channel is reduced, so that more frequency channels can be provided, and frequency efficiency can be increased.
  • a higher transmission rate can be obtained as a whole system.
  • the received signal is converted into a frequency domain signal and separated into signals for each frequency channel, and non-linear repetitive equalization is performed to regenerate the transmission signal. Therefore, the number of subcarriers that can be used for transmission is reduced. Despite being smaller than the number of signals to be transmitted (the number of signals output from the DFT unit), it is possible to transmit without significantly degrading the characteristics.
  • FIG. 3 is a diagram showing an example when subcarriers are applied to a distributed arrangement in the SC-FDMA wireless communication system according to the present invention. It is a block diagram which shows the structure of the terminal device which performs uplink transmission in 1st embodiment of the radio
  • the present invention can accommodate more terminals in a limited band by setting the number of subcarriers constituting one subchannel smaller than the number of signals output in parallel from the DFT section of each terminal.
  • the present invention relates to an SC-FDMA system that can obtain a higher transmission rate, and can greatly improve frequency utilization efficiency as compared with an E-UTRA system.
  • FIG. 1 shows an example when the present invention is applied to a localized arrangement.
  • FIG. 1 shows that the number of frequency signals (spectrums) that are frequency-spread and output in parallel from the DFT part of each terminal is 12 (that is, the DFT size is 12), whereas one subchannel (one frequency) In this example, the number of subcarriers constituting a channel is 10 or 11.
  • the users (users A and G) assigned to the subchannels (frequency channels) at both ends of the band perform transmission of one end (for one subcarrier) of the frequency signals output from the DFT unit.
  • the users (users B to F) assigned to the other subchannels do not transmit the frequency signals (for two subcarriers) at both ends.
  • the clipping process in single carrier transmission assumes that the gain of the frequency characteristic of the propagation path in the subcarrier missing due to clipping is zero, so not only the linear equalization process cannot reproduce, but also the time When the signal is observed, the impulse response of the propagation path becomes long, and the influence of intersymbol interference that the time signal affects the next signal as interference becomes strong.
  • the only way to detect a signal that has spread on the time axis is to reduce the coding rate of the error correction code. As a result, the transmission rate is lowered by the amount of clipping. It will end up.
  • the number of frequency signals to be clipped by the users assigned to the subchannels at both ends of the band and the other subchannels is different is shown.
  • the configuration may be such that the number of frequency signals clipped by the user is the same, and such an example is shown in FIG.
  • the users assigned to the subchannels at both ends of the band also clip the both ends of the frequency signal output from the DFT unit, and the number of subcarriers is smaller than in the case of FIG. It can be seen that 72 subcarriers are all 70 subcarriers in FIG. 2), and that more users can be accommodated while maintaining the transmission rate of each user.
  • FIG. 3 shows an example in which the present invention is applied to a distributed arrangement.
  • FIG. 3 shows the result of clipping the both ends (for two subcarriers) of the frequency signal output from each DFT unit by each user in the distributed arrangement, as in the case shown in FIG. 2 (FIG. 3).
  • 150 indicates a clipped subcarrier). That is, while the number of frequency signals (spectrums) output in parallel from the DFT unit of each user is 12, the number of subcarriers actually transmitted is 10 subcarriers per user. In this way, even by arranging and transmitting a signal obtained by clipping a part of the frequency signal in a distributed arrangement, the transmission rate of each user can be maintained with a smaller number of subcarriers than in the conventional SC-FDMA system. It can accommodate many users.
  • each user clips at least one spectrum at one end (two clipping when clipping at both ends) is shown, but a system with higher frequency utilization efficiency is constructed. In some cases, it may be configured to clip several spectra from the end. However, the number of spectrums to be clipped and their positions (whether only one end or only one end) are preferably determined in advance by the system. In this way, by previously determining the number of spectra to be clipped and their positions, it is not necessary to add extra control information.
  • a guard band a band that does not transmit a signal (subcarrier), which is called a guard band, due to the performance problem of the analog filter. Since signal transmission is not performed at all in this guard band, it is not preferable to provide a guard band from the viewpoint of frequency utilization efficiency.
  • clipping as in the present invention, prevention of frequency utilization efficiency is prevented. You can also. This can be realized by setting the total number of spectra to be clipped after DFT equal to the number of subcarriers to be a guard band.
  • the output frequency signal of the DFT part is defined as the guard band.
  • a signal clipped from the end by the number of subcarriers is transmitted. By performing such clipping, it is possible to transmit the same amount of signals as when no guard band is provided even though the guard band is provided, thereby preventing a decrease in frequency utilization efficiency due to the guard band. be able to.
  • FIG. 4 shows the configuration of a terminal apparatus that performs uplink transmission as described above.
  • transmission section error correction encoding is performed in encoding section 100, and modulation section 101 performs modulation.
  • the modulated transmission signal is serial-parallel converted by the S / P converter 102 and then converted to a frequency domain signal by a DFT (DiscretecreFourier Transform) unit 103.
  • the spectrum clipping unit 104 performs clipping on the frequency signal (spectrum) subjected to time-frequency conversion in this way. This clipping is an operation of deleting several signals (spectrums) from both ends or one end of the output of the DFT unit 103.
  • the number of input / output signals of the spectrum clipping unit 104 is M and N, respectively, M> N holds.
  • the number of signals to be clipped may vary depending on the assigned subchannel, but the spectrum clipping unit 104 performs clipping in consideration of this.
  • a signal obtained by clipping some signals at the end in the spectrum clipping unit 104 is input to the subcarrier mapping unit 105 and assigned to a subcarrier used for transmission.
  • the allocation at this time is performed based on mapping information transmitted from the base station apparatus, received by the receiving antenna unit 112, demodulated by the receiving unit 115 via the radio unit 113 and the A / D conversion unit 114, and used for transmission.
  • Zeros are inserted in subcarriers (other subchannels) that are not received.
  • the number of subcarriers constituting one subchannel is N, which is the same as the number of output signals of the spectrum clipping unit 104.
  • the total transmission power is maintained by adding the power of the previously clipped signal to the signal used for actual transmission (mapped signal).
  • the transmission signal allocated on the subcarrier (subchannel) used for transmission in the subcarrier mapping unit 105 is then input to an IDFT (Inverse Discrete Fourier Transform) unit 106 and a signal in the frequency domain.
  • IDFT Inverse Discrete Fourier Transform
  • the signals of the users multiplexed in the frequency domain use the same time channel.
  • a CP (Cyclic Prefix) insertion unit 108 inserts a CP (a signal obtained by copying the symbol after the IDFT), and the D / A conversion unit 109 converts it into an analog signal.
  • the radio unit 110 up-converts the signal to a radio frequency band signal and transmits the signal from the transmission antenna unit 111.
  • the terminal device In the SC-FDMA system in which the number of subcarriers constituting one subchannel is set to be smaller than the number of signals output in parallel from the DFT unit, the terminal device has the above configuration. Signals can be transmitted without causing interference to other users (using duplicate subcarriers). Further, although the number of subcarriers that can be used for transmission is smaller than the number of signals to be transmitted (the number of signals output from the DFT unit), transmission can be performed without significantly degrading the characteristics.
  • nonlinear iterative equalization for example, frequency domain SC / MMSE (Soft Canceller followed by Minimum Mean Square Error)
  • SC / MMSE Soft Canceller followed by Minimum Mean Square Error
  • FIG. 5 shows a base station apparatus according to the present embodiment.
  • the base station apparatus according to the present embodiment includes a reception antenna unit 200, a radio unit 201, an A / D conversion unit 202, a synchronization unit 203, a CP removal unit 204, an S / P conversion unit 205, a DFT.
  • Unit 206 subcarrier demapping unit 207, zero insertion unit 208, cancellation unit 209, equalization unit 210, IDFT unit 211, demodulation / error correction decoding unit 212, repetition control unit 213, determination unit 214, propagation path estimation unit 215, zero insertion unit 216, propagation path multiplication unit 217, DFT unit 218, replica generation unit 219, scheduling unit 220, transmission unit 221, D / A conversion unit 222, radio unit 223, and transmission antenna unit 224.
  • signals received by receiving antenna section 200 are converted into frequencies that can be A / D converted by radio section 201, and then A / D
  • the conversion unit 202 converts the digital signal.
  • symbol synchronization is established by the synchronization unit 203, and after the CP is removed for each symbol by the CP removal unit 204, the DFT unit 206 passes through the S / P conversion unit 205 and the frequency domain signal from the time domain signal. Each is converted to a signal.
  • the signal converted into the frequency domain signal is separated into signals for each subchannel (user) in the subcarrier demapping unit 207, and the subsequent processing is performed for each received signal of each user.
  • the signal for one subchannel (one user) separated in the subcarrier demapping unit 207 is less than the output of the DFT used on the transmission side, it is clipped on the transmission side by the zero insertion unit 208 Insert zeros in the same frequency component as the signal. This is an operation of adding zeros to both ends or one end of the output signal of the subcarrier demapping unit 207, so that the same number of frequency signals as the DFT output used on the transmission side are added to the zero insertion unit 208. Will be output. This zero insertion is also performed in the zero insertion unit 216 with respect to the propagation channel estimation value calculated in the propagation channel estimation unit 215 using the pilot signal for propagation channel estimation.
  • equalization is performed by treating the spectrum clipped on the transmission side as if it has been lost due to a drop in the propagation path.
  • the zero insertion unit 208 is also provided after the subcarrier demapping unit 207, but this is not essential. This is because zero insertion is performed on the pilot signal for propagation path estimation in the zero insertion unit 216, so that the clipped spectrum is treated as 0 even without the zero insertion unit 208 and is synthesized in the equalization unit 210. This is because there is nothing.
  • the output signal of the zero insertion unit 208 is input to the cancellation unit 209, and zero is set at the position of the clipped spectrum and the soft replica of the transmission signal generated by the replica generation unit 219 based on the reliability of the own signal.
  • a soft replica of the received signal calculated by multiplication of the inserted propagation path estimation value (calculated by the propagation path multiplication unit 217) is subtracted.
  • the soft replica of the received signal is once canceled from the received signal, and the residual signal component is calculated.
  • the equalization unit 210 (to be described later) performs an inverse matrix operation, so if the cancellation and equalization are repeated leaving only the desired signal, the inverse matrix operation is performed at least as many times as the desired signal included in the block.
  • the residual signals can be handled in common within the block, and all weights can be calculated by performing an inverse matrix operation once within the block. For this reason, the amount of computation associated with the inverse matrix computation is reduced by separately inputting a soft replica of the transmission signal to the equalization unit 210 and reconfiguring it.
  • the cancel process is not performed and the received signal is sent to the equalization unit 210 as it is.
  • the equalization unit 210 performs signal equalization using the residual component output from the cancellation unit 209, the propagation path estimation value of the desired signal, and the desired signal soft replica. Specifically, the equalization unit 210 calculates optimal weights from residual components, propagation path estimation values, and signal soft replicas, and outputs a final time-equalized signal multiplied by the optimal weights. is doing. However, since the soft replica is not input in the case of the first processing, this is equivalent to the conventional MMSE equalization without cancellation.
  • the equalized signal is converted into a time-domain signal by the IDFT unit 211, and then demodulated and error-corrected by the demodulation / error correction decoding unit 212. Then, the demodulation / error correction decoding unit 212 outputs an outer log likelihood ratio (LLR: Log Likelihood Ratio) of the sign bit with improved reliability.
  • LLR Log Likelihood Ratio
  • the external LLR represents reliability improved only by error correction processing.
  • the external LLR output from the demodulation / error correction decoding unit 212 is controlled by the iterative control unit 212 to determine whether or not to repeat the process.
  • the replica LLR 219 When the process is repeated, the replica LLR 219 generates a soft replica of the signal. Entered. As described above, the replica generation unit 219 generates a soft replica proportional to the reliability according to the LLR of the sign bit.
  • the soft replica generated in this way is sent to the DFT unit 218 for once canceling the received signal component to which the desired frequency signal contributes in the cancel unit 209, and so on for reconfiguring the desired signal at the time of equalization. Is input to the conversion unit 210.
  • an example of a base station configuration in which received signals of respective users (subchannels) are sequentially selected and processing for the selected signals is serially illustrated, but the zero insertion unit 208, the cancellation unit 209, etc.
  • the predetermined number of repetitions may be fixed, or adaptive control such as repetition until there is no error in the result of the demodulation / error correction decoding unit 212 is possible.
  • the number of repetitions in the receiving apparatus may be set to be different for each subchannel.
  • the reception level measurement pilot signal is sent from the DFT unit 206 to the scheduling unit 220.
  • the scheduling unit 220 Based on the measurement result of the reception level using this signal, the scheduling unit 220 performs scheduling in consideration of the propagation status of each user (determination of which user is assigned to which subchannel). In this scheduling, by assigning each user to a subchannel with better propagation path conditions and obtaining gain due to multiuser diversity, better reception characteristics can be obtained even when a part of the spectrum at the end is clipped. Can do.
  • the mapping information determined in the scheduling unit 220 is modulated in the transmission unit 221, passes through the D / A conversion unit 222, the radio unit 223, and the like, and is transmitted from the transmission antenna unit 224 to each user. This mapping information is used for transmission from each user after the next frame. Further, it is also used for processing of subcarriers for each subchannel in the subcarrier demapping unit 207 when receiving a corresponding frame.
  • FIG. 6 shows the relationship between frames and subchannels in this embodiment.
  • each frame is composed of a plurality of symbols.
  • a different number of subchannels is provided for each frame by clipping a different number of frequency signals for each frame.
  • the number of frequency signals clipped by each user assigned to frame 1 in FIG. 6 is 2, and 7 subchannels can be provided, whereas in frame 2, each user does not perform clipping, and the subchannel The number is six.
  • the number of subchannels in frame 3 is 8, and each user assigned to this frame clips three frequency signals. In this way, by setting the number of frequency signals to be clipped differently for each frame, a different number of subchannels can be provided for each frame, and a system that can flexibly use limited resources is constructed. Is possible.
  • reception characteristics usually deteriorate as the number of frequency signals to be clipped increases.
  • users assigned to each frame It is possible to prevent degradation of reception characteristics by adaptively selecting. For example, among users to be allocated, a user with a better propagation path condition is allocated to a frame with a large number of clippings, and a user with a poor propagation path condition is allocated to a frame with a small number of clippings (or no clipping). That's it.
  • some threshold values relating to the received SNR may be set in advance, and these threshold values may be associated with the number of clippings. However, a larger number of clippings is set to a higher threshold.
  • the reception characteristics greatly depend on not only the value of the received SNR but also the fluctuation state on the frequency axis of the propagation path. This is because the influence of intersymbol interference is small when the frequency response of the assigned propagation path is relatively flat, whereas the influence of intersymbol interference is large when the frequency response varies greatly. It is by receiving. Therefore, considering not only the received SNR but also the frequency response of the propagation path, when the frequency response of the assigned propagation path is relatively flat, it is assigned and assigned to a frame composed of subchannels with a large number of clippings. When the frequency response of the propagation path is not flat, it is possible to further improve the reception characteristics by assigning to a frame composed of subchannels with a small number of clippings.
  • an index indicating the fluctuation state of the frequency response of the propagation path there are, for example, delay time and power of a delay wave, and a user who uses a propagation path having a delay wave with high power and a long delay time has a small number of clippings.
  • Allocating to a frame subchannel composed of subchannels a user who uses a propagation path with few high-power delayed waves is allocated to a frame composed of subchannels with a large number of clippings.
  • the propagation state of the propagation path can be grasped to some extent by simple control such as calculating the number of subcarriers that are lower than the average power level of the subchannel.
  • the propagation path of the subchannel is relatively flat, and is assigned to a frame composed of subchannels with a large number of clippings.
  • a frame to be allocated may be selected according to the position of each user in the cell. This is effective in a system in which the target value of transmission power control for users close to the base station is higher than the target value for users far from the base station. A user far from the base station is assigned to a frame with a small number of clippings.
  • EXIT chart EXtrinsic Information Transfer chart
  • the horizontal axis represents the equalization unit input mutual information amount
  • the vertical axis represents the equalization unit output mutual information amount.
  • the mutual information amount output from the equalization unit is input to the decoding unit, so that the vertical axis coincides with the decoding unit input mutual information amount.
  • the horizontal axis corresponds to the mutual information amount of the decoding unit.
  • the mutual information amount is the amount of information that can be obtained from Y with respect to X when a certain signal X is sent and the received signal Y is obtained.
  • the maximum value is constrained to 1.
  • the line 300 is the input / output relationship of the mutual information amount in the decoding unit with the vertical axis as the input and the horizontal axis as the output, and as the coding rate increases, much power is required for decoding.
  • the line translates upward in the figure.
  • a line 301 represents the input / output relationship of the mutual information amount in the equalization unit with the horizontal axis as input and the horizontal axis as output.
  • the line 300 indicating the input / output characteristics of the decoding unit is uniquely determined with respect to the structure of the error correction code to be used, it is possible to know the characteristics before iterative processing.
  • the line 301 indicating the input / output characteristics of the equalizer is determined by the propagation path characteristics and the SNR, details cannot be drawn in advance.
  • the value of the input external mutual information amount 0 of the equalization unit point A in FIG. 7 and this position is referred to as the start point
  • the value of the input external mutual information amount 1 point F in FIG. 7
  • This position is referred to as the end point
  • the approximation characteristic 301 of the equalizer can be calculated by approximating the start point and the end point with a straight line.
  • the mutual information amount of input is 0 in the first process
  • the mutual information amount of point A is obtained as the output of the equalization unit.
  • the output mutual information amount of this equalization unit becomes the input mutual information amount to the decoding unit, it moves like a dotted line, and the output mutual information amount of the decoding unit comes to point B.
  • the end point of the equalizer characteristic means that all the interference components have been removed, and the characteristic is determined only by the received power and noise power of only the desired signal.
  • the intersymbol interference enhanced by clipping can be completely removed.
  • a dotted line representing this movement is called an EXIT trajectory.
  • FIG. 8 shows a statistical EXIT locus when the number of frequency signals to be clipped is changed.
  • the line 303 in FIG. 8 indicates the equalization characteristic when the clipping number is M
  • the line 304 indicates the equalization characteristic when the clipping number is N (M> N)
  • the line 302 indicates the decoding characteristic.
  • the starting point of the equalization unit characteristic is lowered. This shows that the influence of stronger intersymbol interference is manifested by the large number of clippings. This indicates that the interference cannot be removed at the first stage of the iterative process.
  • the end point is a characteristic when the influence of intersymbol interference due to clipping is removed by iterative processing, it matches on average (in lines 304 and 302) regardless of the number of clipping.
  • the line 304 of the equalization unit is above the line 302 of the decoding unit, and therefore can be separated by repetition.
  • the line 303 of the equalization unit crosses the line 302 of the decoding unit, and the mutual information beyond the crossed point cannot be obtained. That is, the intersymbol interference is so strong that it cannot be removed even if iterative processing is performed. Therefore, in this case, it is possible to design the number of frequency signals clipped by each user as N, and the number of subchannels can be adjusted accordingly.
  • the number of frequency signals to be clipped can be set adaptively by drawing the EXIT trajectory as a trajectory with respect to the instantaneous propagation path fluctuation in units such as every frame instead of a statistical one like the 1% value.
  • the EXIT trajectory of the equalization unit when the number of clippings is changed is drawn as described above, and the line of the decoding unit The number of clippings that do not cross will be selected. For example, a user assigned to a subchannel with good propagation path conditions sets a larger number of clippings, and a user assigned to a subchannel with poor propagation path conditions sets a smaller number of clippings.
  • the DFT size of each user can be changed according to the number of clippings (the DFT size is increased when the number of clippings is large, and the DFT size is decreased when the number of clippings is small).
  • the number of clippings it is possible to construct a system that can realize different transmission rates for each subchannel (each user) even if the number of subcarriers constituting each subchannel is the same. it can.
  • this is a coding rate that does not cross the line 307 of the equalization unit (in this case, the line 306 of the coding rate L does not cross.
  • the line 305 of the coding rate K crosses.
  • this can be achieved by setting K> L) and increasing the resistance to interference that cannot be removed in the first iteration.
  • the coding rate is shown here, the coding method (turbo code, convolutional code, low density parity check (LDPC) code, etc.) can be changed and designed. The flexibility when designing can be increased.
  • Such selection of coding rate and coding method can also be performed adaptively by drawing an EXIT locus on the base station side in units such as every frame.
  • the above embodiments are directed to the SC-FDMA scheme that generates a spread spectrum signal using DFT, but unlike this, a scheme that generates a spread spectrum signal by multiplying a spread code (for example, MC- (CDMA system) also, it is sufficient to delete a part of the end of the signal after frequency spreading on the transmission side, insert zero on the reception side at the position of the signal deleted on the transmission side, and perform repeated equalization processing,
  • MC- CDMA system

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PCT/JP2009/058009 2008-04-22 2009-04-22 無線通信システム及びにそれに用いる送信装置 Ceased WO2009131155A1 (ja)

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