WO2014057840A1 - 端末装置、基地局装置、無線通信システム、受信方法および集積回路 - Google Patents
端末装置、基地局装置、無線通信システム、受信方法および集積回路 Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
- H04B7/0621—Feedback content
- H04B7/0626—Channel coefficients, e.g. channel state information [CSI]
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/0413—MIMO systems
- H04B7/0417—Feedback systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/0413—MIMO systems
- H04B7/0452—Multi-user MIMO systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/0413—MIMO systems
- H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
- H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
- H04B7/0842—Weighted combining
- H04B7/0845—Weighted combining per branch equalization, e.g. by an FIR-filter or RAKE receiver per antenna branch
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/20—Control channels or signalling for resource management
Definitions
- the present invention relates to a technique for performing multiuser multiple input multiple output transmission.
- MIMO Multiple input multiple output
- MU-MIMO Multi User-MIMO
- IUI inter-user-interference
- the base station device pre-multiplies a linear filter calculated based on the propagation path information notified from each terminal device.
- linear precoding that suppresses the IUI is employed.
- MU-MIMO technology using nonlinear precoding in which nonlinear processing is performed on the base station apparatus side is attracting attention.
- the terminal device If the terminal device is capable of modulo operation, it can add a perturbation vector whose element is a complex number (perturbation term) obtained by multiplying an arbitrary Gaussian integer by a constant real number to the transmitted signal. It becomes.
- Non-Patent Document 1 Vector perturbation (VP) described in Non-Patent Document 1 and Tomlinson Harashima precoding (THP) described in Non-Patent Document 2 are well known as methods capable of realizing optimal transmission characteristics.
- VP Vector perturbation
- THP Tomlinson Harashima precoding
- the accuracy of precoding largely depends on the precision of propagation path information (Channel state information (CSI)) that can be grasped by the base station apparatus.
- CSI propagation path information
- the base station apparatus feeds back CSI estimated by the terminal apparatus to the base station apparatus, so that the base station apparatus I can grasp it.
- an error may occur between the CSI that can be grasped by the base station apparatus and the actual CSI. This will be briefly described with reference to FIG.
- FIG. 11 is a sequence chart showing a state of communication between a base station apparatus that performs precoding and a terminal apparatus.
- the base station apparatus transmits a reference signal for estimating CSI to the terminal apparatus (step S1). Further, the base station apparatus generates transmission data and a demodulation reference signal (step S2). Since the reference signal is known to the base station device and the terminal device, the terminal device can estimate the CSI based on the received reference signal (step S3).
- the CSI error that occurs depending on the time selectivity of the propagation path is referred to as a time variation error, and the quantization error and the time variation error are collectively referred to as a feedback error. Since the CSI that can be grasped by the base station apparatus includes a feedback error, it is extremely difficult for the base station apparatus to acquire a highly accurate CSI.
- FIG. 12 is a sequence chart showing a state of communication between a base station apparatus that performs precoding and a terminal apparatus.
- time division duplexing uplink transmission and downlink transmission are separated by time and transmitted.
- the uplink transmission signal includes a reference signal for signal demodulation, and the base station apparatus acquires CSI from the reference signal and performs signal demodulation (step T2).
- the base station apparatus precodes the downlink transmission signal.
- the base station apparatus since there is duality between the uplink propagation path and the downlink propagation path, the base station apparatus previously acquired the CSI obtained for demodulating the uplink transmission signal. Based on the above, precoding can be performed (step T3). Then, data is transmitted to the terminal device (step T4). On the other hand, in the terminal device, propagation path estimation and downlink signal demodulation are performed (step T5).
- Non-Patent Document 3 For the purpose of improving the transmission characteristics of precoding transmission in an environment where the influence of the feedback error of CSI is large as described above, in Non-Patent Document 3, the received signal subjected to precoding is a terminal.
- the terminal device re-estimates the propagation path information at the time when it is received by the device, and performs transmission based on feedback error by performing appropriate channel equalization processing on the received signal again based on the propagation path information. Methods for improving the deterioration of characteristics are discussed.
- the method according to Non-Patent Document 3 assumes a case in which only one data stream is sent to each terminal device, and precoding considers only linear precoding.
- the terminal device of the present invention includes a feedback information generation unit that generates feedback information including propagation path information at the second time, a radio transmission unit that notifies the base station device of the feedback information, Is further provided.
- the linear filter is calculated based on propagation path information at the second time.
- the base station apparatus of the present invention includes a plurality of antennas according to any one of (1) to (6) described above at a first time for a radio signal obtained by performing nonlinear precoding and spatial multiplexing.
- Base station apparatus that transmits to the terminal apparatus, and performs nonlinear precoding on a signal transmitted to each terminal apparatus based on propagation path information at a second time that is past the first time.
- the base station apparatus of the present invention includes a receiving unit that receives a radio signal including a reference signal from the terminal apparatus at the second time, and a reference signal that separates the reference signal from the received radio signal.
- a separation unit, and an estimation unit that estimates propagation path information between the terminal device at the second time based on the reference signal, and the non-linear precoding unit at the second time Based on propagation path information with the terminal device, nonlinear precoding is performed on a signal to be transmitted to the terminal device.
- the wireless communication system of the present invention is characterized by comprising the terminal device described in (1) above and the base station device described in (7) above.
- AT is a transposed matrix of matrix A
- a H is an adjoint (Hermitian transposed) matrix of matrix A
- a ⁇ 1 is an inverse matrix of matrix A
- a + is a pseudo ( Or, general) Inverse matrix
- diag (A) is a diagonal matrix obtained by extracting only the diagonal components of matrix A
- floor (c) is such that the real part and imaginary part do not exceed the values of the real part and imaginary part of complex number c, respectively.
- a floor function that returns the largest Gaussian integer E [x] is an ensemble average of the random variable x
- abs (c) is a function that returns the amplitude of the complex number c
- angle (c) is a function that returns the argument of the complex number c
- represents the norm of the vector a
- x% y represents the remainder when the integer x is divided by the integer y
- n C m represents the total number of combinations for selecting different m from different n.
- [A; B] represents a matrix obtained by combining two matrices A and B in the row direction
- [A, B] represents a matrix obtained by combining the matrices A and B in the column direction.
- Z [i] represents a set of all Gaussian integers.
- a Gaussian integer represents a complex number in which the real part and the imaginary part are each represented by an integer.
- FIG. 1 is a diagram showing an outline of a radio communication system according to the first embodiment of the present invention.
- N t has transmit antennas, relative to the non-linear precoding capable base station apparatus 1 (also referred to as a wireless transmitting device), the terminal apparatus 2 having the receive antennas N r the (This is also referred to as a wireless reception device.
- terminal devices 2-1 to 2-4 are shown. These are hereinafter also referred to as terminal devices.)
- orthogonal frequency division multiplexing OFDM
- OFDM orthogonal frequency division multiplexing
- signal processing described below is performed for each subcarrier.
- the duplex method is assumed to be Frequency Division Duplex (FDD).
- the base station device 1 acquires channel state information (Channel State Information (CSI)) to each terminal device from the control information notified from each terminal device 2-1 to 2-4, and transmits based on the channel information. It is assumed that data is precoded for each subcarrier.
- CSI Channel State Information
- the u-th terminal device estimates CSI h u (k, t 1 ) at time t 1 .
- the u-th terminal device can notify CSI h u (k, t 1 ) in a state close to an ideal value for the base station device.
- FIG. 2 is a block diagram showing the configuration of the base station apparatus according to the first embodiment of the present invention.
- the base station apparatus 1 includes a channel encoding unit 21, a data modulation unit 23, a mapping unit 25, a precoding unit (nonlinear precoding unit) 27, an antenna unit 29, and control information.
- An acquisition unit 31, a propagation path information acquisition unit 33, and a control information generation unit 35 are included.
- Precoding unit 27 is the number of subcarriers N c
- the antenna unit 29 is present respectively by the number of transmit antennas N t.
- control information acquisition unit 31 acquires control information notified from each of the connected terminal devices 2-1 to 2-4, of which information associated with the propagation path information is transmitted to the propagation path information acquisition unit. Output to 33.
- the propagation path information acquisition unit 33 acquires the propagation path matrix H (k, t 1 ) based on the input information and outputs it to the precoding unit 27.
- the data modulation unit 23 performs digital data modulation such as QPSK and 16QAM. .
- the data modulation unit 23 inputs the data signal subjected to data modulation to the mapping unit 25.
- the reference signals addressed to the respective terminal devices 2-1 to 2-4 are multiplexed so as to be orthogonal to each other so that they can be separated in the received terminal device.
- the CSI-reference signal which is a reference signal for propagation path estimation
- another reference signal may be further multiplexed.
- CSI-RS is for estimating a channel matrix observed in each terminal apparatus.
- the mapping unit 25 performs mapping so that the data signal and the CSI-RS are transmitted at different times or frequencies.
- the mapping unit 25 arranges the CSI-RS so as to be orthogonal between the transmission antennas.
- the mapping unit 25 inputs the mapped data information or the like to the corresponding subcarrier precoding unit 27.
- the subcarrier index k and the time indexes t 1 and t 2 are omitted.
- the precoding unit 27 first calculates a linear filter W for suppressing IUI in the linear filter generation unit 27-1.
- the calculation method of the linear filter W is not limited to anything.
- ⁇ is a control term for controlling the size of the residual IUI. It is determined based on transmission power, the number of spatially multiplexed terminals, desired reception quality, and the like. For example, it is a reciprocal of an average received signal-to-noise power ratio (SNR) per terminal apparatus.
- SNR average received signal-to-noise power ratio
- a linear filter W that minimizes the sum of the mean square errors of a plurality of subcarriers may be calculated.
- the linear filter W is calculated for each subcarrier.
- the same linear filter may be used for a plurality of subcarriers.
- the linear filter generation unit 27-1 outputs the calculated linear filter W to the perturbation vector search unit 27-2, the transmission signal generation unit 27-3, and the control information generation unit 35, respectively.
- the power normalization coefficient ⁇ is given by equation (2).
- the linear filter W In order to make the linear filter W an orthogonal matrix, it is only necessary to appropriately combine combinations of terminal devices that are spatially multiplexed. However, such control is performed in accordance with communication opportunities of the terminal devices 2-1 to 2-4. Since fairness is lowered, it is desirable not to limit the combination of terminal devices. Further, when the number of terminal devices connected to the base station device 1 is small, there may be no combination of terminal devices in which the linear filter W is an orthogonal matrix. As a method of avoiding an increase in required transmission power, a method of adding a perturbation term to transmission data can be considered. Precoding on the premise that a perturbation term is added to transmission data is called nonlinear precoding.
- the perturbation term is expressed as a complex number obtained by multiplying a predetermined real number 2 ⁇ by an arbitrary Gaussian integer.
- the terminal device performs signal processing called modulo operation (also called modulo operation or remainder operation) on the received signal, so that the perturbation term can be removed.
- the real number 2 ⁇ is also called a modulo width and may be any value as long as it is shared between the base station apparatus 1 and the terminal apparatuses 2-1 to 2-4, but the M value of the minimum signal point distance is ⁇ .
- 2 ⁇ ⁇ ⁇ M 1/2 .
- 2 ⁇ 2 ⁇ 2 1/2 for QPSK (4QAM) modulation
- 2 ⁇ 8 ⁇ 10 ⁇ 1/2 for 16QAM modulation.
- the perturbation vector search unit 27-2 searches for perturbation terms that can maximize the power normalization term ⁇ from innumerable perturbation terms, and adds them to the transmission data, so that it is always constant regardless of the combination of terminal devices. Reception quality can be maintained.
- the perturbation term to be searched by the base station apparatus 1 is to minimize the required transmission power, but the perturbation term that can achieve the desired quality and frequency utilization efficiency is searched. Also good.
- the base station apparatus 1 searches for the perturbation term in all subcarriers. However, it is not necessary to search for the perturbation term for some subcarriers.
- the base station apparatus 1 can add a perturbation term to each. Further, since the perturbation terms are selected from arbitrary Gaussian integers, even if the number of selectable Gaussian integers is limited to K, all combinations of perturbation terms that can be added to the transmission data by the base station apparatus 1 are all. also extends to K U Street. So exploring everything is not practical. Therefore, the number of selectable Gaussian integers should be extremely reduced, or perturbation terms with required transmission power exceeding a certain level should be excluded from the search candidates (this method is called Sphere encoding). It is necessary to limit the number of combinations.
- the perturbation term search method is not limited to anything.
- the perturbation term may be searched based on Sphere encoding.
- the perturbation vector search unit 27-2 has searched for an optimal perturbation term by some method.
- 2 ⁇ z u represents a perturbation term added to transmission data addressed to the u-th terminal device. At this time, z satisfies Expression (3).
- the transmission signal generation unit 27-3 performs transmission based on the linear filter W calculated by the linear filter generation unit 27-1, the perturbation vector z calculated by the perturbation vector search unit 27-2, and the transmission data vector d.
- the signal vector s ⁇ W (d + 2 ⁇ z) is calculated. Note that the power normalization term ⁇ at this time is newly calculated in consideration of the perturbation vector z. In the following, the linear filter is considered including the power normalization term ⁇ .
- transmission power normalization is performed for each subcarrier.
- power normalization may be performed so that the total transmission power of a plurality of subcarriers and OFDM signals is constant.
- the search for the perturbation vector z may also be controlled in consideration of the total required transmission power.
- the transmission signal vector calculated by the transmission signal generation unit 27-3 is input to the antenna unit 29 as the output of the precoding unit 27.
- the precoding process is not performed, and only the transmission power is adjusted and output to the antenna unit 29. Further, the precoding unit 27 outputs the linear filter W calculated by the linear filter generation unit 27-1 toward the control information generation unit 35.
- w u is a linear filter by which transmission data addressed to the u-th terminal device is multiplied, and is represented by a matrix of N t rows and L columns.
- the information to be notified to the u th terminal device is w u .
- the control information generation unit 35 performs quantization on w u .
- the quantization method is not limited to anything. For example, a method of directly quantizing each element of w u with a finite bit length and notifying the terminal device of the quantized information can be considered. Further, with respect to w u, applying the information compression technology used in wireless LAN standard 802.11n (Non-compressed feedback scheme or Compressed? Feedback method), it may be to compress the amount of information relating to the notification .
- a code book describing a plurality of linear filters is shared in advance between the base station device 1 and each of the terminal devices 2-1 to 2-4, and is closest to w u among the linear filters described in the code book.
- the linear filter may be searched and the index may be notified.
- the code book may be different for each terminal device, and control may be performed so that the linear filter described in the code book is updated at a certain period.
- this code book may be used for notification of the linear filter.
- the control information generation unit 35 quantizes w u into information that can be notified to the u th terminal device, and the quantized signal is transmitted to a radio transmission unit (described later) of the antenna unit 29 ( The data is output to (transmission unit) 29-3. Therefore, the control information generation unit 35 may convert the quantized signal into a signal suitable for input to the wireless transmission unit 29-3 in advance. For example, an OFDM signal including a quantized signal may be generated and output to the wireless transmission unit 29-3. Moreover, you may control to transmit together with another control information.
- FIG. 4 is a block diagram showing a device configuration of the antenna unit 29 according to the first embodiment of the present invention.
- the antenna unit 29 includes an IFFT unit 29-1, a GI insertion unit 29-2, a radio transmission unit 29-3, a radio reception unit (reception unit) 29-4, and an antenna 29- 5.
- the IFFT unit 29-1 performs N c -point inverse fast Fourier transform (IFFT) or inverse discrete Fourier transform (IDFT) on the signal output from the corresponding precoding unit 27.
- IFFT inverse fast Fourier transform
- IDFT inverse discrete Fourier transform
- the GI insertion unit 29-2 gives a guard interval to the input OFDM signal, and then inputs it to the radio transmission unit 29-3.
- the radio transmission unit 29-3 converts the input baseband transmission signal into a radio frequency (RF) transmission signal and inputs the transmission signal to the antenna 29-5.
- the antenna 29-5 transmits the input transmission signal in the RF band.
- FIG. 5 is a block diagram showing the configuration of the terminal apparatus according to the first embodiment of the present invention.
- the terminal apparatus includes a terminal antenna unit 51, a propagation path estimation unit 53, a feedback information generation unit 55, a channel equalization unit 57, a demapping unit 59, a data demodulation unit 61, and a channel decoding. Part 63.
- FIG. 6 is a block diagram showing a configuration of the terminal antenna unit 51 according to the first embodiment of the present invention.
- the terminal antenna unit 51 includes a radio reception unit 51-1, a radio transmission unit 51-2, a GI removal unit 51-3, an FFT unit 51-4, and a reference signal separation unit 51-. 5, a control information acquisition unit 51-6, and an antenna 51-7.
- the transmission signal transmitted from the base station apparatus 1 is first received by the antenna 51-7 of each terminal antenna unit 51 and then input to the radio reception unit 51-1.
- the wireless reception unit 51-1 converts the input signal into a baseband signal, and outputs a signal related to the data signal and the reference signal (CSI-RS) to the GI removal unit 51-3.
- CSI-RS data signal and the reference signal
- a signal related to control information is output to the control information acquisition unit 51-6.
- the GI removal unit 51-3 removes the guard interval from the input signal and inputs the guard interval to the FFT unit 51-4.
- FFT unit 51-4 to the input signal, after applying fast Fourier transform of N c point (FFT) or discrete Fourier transform (DFT), was converted to N c subcarrier component, the reference signal
- the data is input to the separation unit 51-5.
- the reference signal separation unit 51-5 separates the input signal into a data signal component and a reference signal (CSI-RS) component.
- the reference signal separation unit 51-5 inputs the data signal component to the channel equalization unit 57, and inputs the CSI-RS to the propagation path estimation unit 53.
- the signal processing described below is basically performed for each subcarrier.
- control information acquisition unit 51-6 a signal associated with the linear filter generated by the precoding unit 27 of the base station device 1 (control information of the base station device 1) is input from the signal input from the wireless reception unit 51-1.
- the signal generated by the generation unit 35) is acquired, and a linear filter (w u for the u-th terminal device) multiplied by the transmission data addressed to the own device is calculated.
- w u for the u-th terminal device
- the control information acquisition unit 51-6 outputs the calculated w u to the propagation path estimation unit 53.
- the propagation path estimation unit 53 performs propagation path estimation based on the inputted known reference signal CSI-RS. Since the CSI-RS is transmitted without applying precoding, the matrix h u (corresponding to each terminal device among the channel matrix H (k, t 2 ) represented by the equation (1). k, t 2 ) can be estimated. Normally, since CSI-RS is intermittently multiplexed with respect to radio resources, propagation path information of all subcarriers cannot be estimated directly, but at time intervals and frequency intervals that satisfy the sampling theorem. By transmitting CSI-RS, it is possible to estimate channel information of all subcarriers by appropriate interpolation. A specific propagation path estimation method is not particularly limited. For example, two-dimensional MMSE propagation path estimation may be used.
- the propagation path estimation unit 53 inputs the propagation path information estimated based on the CSI-RS to the feedback information generation unit 55.
- the feedback information generation unit 55 generates information to be fed back to the base station apparatus 1 in accordance with the input propagation path information and the propagation path information format fed back by the terminal apparatuses 2-1 to 2-4.
- the propagation path information format is not limited to anything.
- the terminal device quantizes the propagation path information estimated for each subcarrier or for each resource block in which a plurality of subcarriers are collected with a finite number of bits and feeds back the quantization information.
- feedback may be performed based on a code book that has been agreed with the base station apparatus 1 in advance.
- the feedback information generation unit 55 may perform quantization after performing some signal conversion instead of directly quantizing the propagation path information.
- signal conversion for example, a method of performing singular value decomposition is conceivable.
- the feedback information generation unit 55 generates information to be notified to the base station apparatus 1 by quantizing the eigenvector obtained by the singular value decomposition or both the eigenvector and the singular value.
- the propagation path information is all subcarriers, that is, the propagation path information in the frequency domain is used.
- the feedback information generation unit 55 performs inverse discrete Fourier transform or inverse discrete cosine transform on the propagation path information estimated in the frequency domain, thereby converting the propagation path information into time domain propagation path information, and then performing quantization. You may give it. Further, the feedback information generation unit 55 may perform control such that only a part of the propagation path information converted into the time domain is fed back.
- the feedback information generation unit 55 may generate feedback information based on propagation path information obtained by performing extrapolation based on a plurality of propagation path information acquired up to time t 1. .
- the coefficient of the polynomial used for interpolation may be used as feedback information.
- the terminal device 2 performs linear linear prediction of the propagation path information H (t) at time t
- a and B are calculated for each complex channel gain of each antenna and each discrete path based on the least square method, the mean square error minimum method, or the like.
- the feedback information generation unit 55 may use A and B calculated for each antenna and each complex channel gain of each discrete path as feedback information.
- prediction of propagation path information may be performed in the frequency domain.
- the terminal device 2 may perform linear prediction for each subcarrier, or may perform linear prediction for each resource block in which a plurality of subcarriers are collected. Even in this case, the terminal device 2 may use the coefficient of the polynomial used for the prediction as feedback information instead of the predicted propagation path information itself.
- the information that can be notified as feedback information by the terminal apparatus 2 is diverse, but if the information format of feedback is shared between the base station apparatus 1 and the terminal apparatus 2, the base station The device 1 can acquire channel information based on the fed back information.
- the feedback information generation unit 55 inputs the generated signal to the wireless transmission unit 51-2 of each terminal antenna unit 51.
- the wireless transmission unit 51-2 converts the input signal into a signal suitable for notifying the base station apparatus 1 and inputs the signal to the antenna 51-7 of the terminal antenna unit 51.
- the antenna 51-7 transmits the input signal toward the base station apparatus 1.
- the amplitude and phase of the desired signal fluctuate due to the influence of the time and frequency selectivity of the propagation path. Therefore, in order to correctly demodulate the desired signal, channel equalization processing that removes this influence is required. In order to perform channel equalization processing, it is necessary to estimate the channel gain that affects the amplitude and phase of the signal.
- the propagation path gain h u (t 2 ) has already been acquired by the propagation path estimation unit 53.
- h u (t 2 ) ⁇ w u affects the desired signal.
- the base station apparatus transmits a demodulation reference signal (DMRS) in addition to CSI-RS as a reference signal.
- DMRS demodulation reference signal
- the DMRS is transmitted after being multiplied by the linear filter W, and since the DMRS is transmitted with radio resources that are orthogonal or pseudo-orthogonal between the terminal apparatuses, each terminal apparatus performs channel equalization. Necessary h u (t 2 ) ⁇ w u can be estimated.
- Equation (4) the first term is the desired signal component, the second term is the residual IUI component, and the third term is the noise component. It can be seen that dividing the equation (4) by h u (t 2 ) ⁇ w u estimated by DMRS can compensate for the effects of phase and amplitude variations on the desired signal.
- the desired signal is composed of the desired data signal du and a perturbation term z u added to the desired data signal. This perturbation term can be removed by a modulo operation described later. However, the perturbation term added to the transmission data addressed to the other terminal device included in the residual IUI cannot be removed by the modulo calculation. Therefore, if channel equalization is performed based on the channel estimation value obtained by DMRS, the transmission characteristics are significantly degraded.
- the terminal rather than performing demodulation based on DMRS, consider that performs signal demodulation based on the linear filter w u notified from the base station apparatus 1.
- the propagation path estimation unit 53 can estimate h u (t 2 ), which is propagation path information not subjected to precoding, by CSI-RS. Therefore, the propagation path estimation unit 53 multiplies the estimated h u (t 2 ) by the w u notified from the base station apparatus 1, and the same propagation path information h u (t 2 ) as the value estimated by the DMRS. Xw u can be estimated. However, if signal demodulation is performed based on this information, a large residual IUI is generated.
- the channel estimation unit 53 by multiplying the notified w u from the base station apparatus 1 to h u (t 1) which is estimated on the basis of the CSI-RS received at time t 1 h u (t 1 ) w u is output to the channel equalization unit 57 as a channel estimation value.
- the channel equalization unit 57 performs channel equalization on the received signal based on h u (t 1 ) w u input from the propagation path estimation unit 53.
- Expression (4) can be expressed as Expression (5) (the noise term is omitted).
- the first term is a desired signal component
- the second term is a residual IUI generated at the time of precoding
- the third term is a residual IUI generated due to propagation path fluctuation.
- the channel equalization unit 57 performs channel equalization by dividing Equation (5) by h u (t 1 ) w u . Note that channel equalization is not limited to this method.
- the signal after channel equalization is given by equation (6).
- the non-linear precoding performed in the precoding device of the base station device 1 aims to minimize
- the error vector also includes the effect of phase rotation caused by the difference in frequency between the oscillator of the base station apparatus 1 and the oscillators of the terminal apparatuses 2-1 to 2-4. Will be performed. If this phase rotation can be estimated by another method, it may be controlled to perform equalization in consideration of the effect of phase rotation at the time of channel equalization.
- the base station device 1 that performs a precoding for transmit data to be transmitted at time t 2 based on the CSI notified at time t 1 terminal devices 2-1 to 2-
- the terminal devices 2-1 to 2-4 do not know at what time the precoding performed by the base station device 1 is based on the notified CSI. Cases are also conceivable. Therefore, the precoding unit 27 of the base station apparatus 1 outputs information associated with the linear filter used for precoding to the control information generating unit 35, and further, the CSI used for precoding is A configuration may be adopted in which control information that indicates what time is notified from the terminal devices 2-1 to 2-4 is output to the control information generation unit 35.
- the base station apparatus 1 sets the value of ⁇ to the terminal apparatuses 2-1 to 2-2. -4 may be notified.
- the terminal devices 2-1 to 2-4 may perform control so as to estimate ⁇ .
- the base station apparatus 1 notifies the linear filters w u to the terminal apparatuses 2-1 to 2-4, and the terminal apparatuses 2-1 to 2-4 have estimated by the own apparatus.
- the base station apparatus 1 uses h u (t 1 ) w u instead of the linear filter w u.
- the terminal device 2-1 to 2-4 may be notified directly.
- the terminal devices 2-1 to 2-4 may be configured to further perform signal processing on h u (t 1 ) w u notified from the base station device 1.
- the CSI that can be notified by the terminal devices 2-1 to 2-4 includes information on long-period fluctuations in the propagation path such as propagation loss between the base station device 1 and the terminal devices 2-1 to 2-4. This is because it may not be included.
- the channel equalization unit 57 further performs a modulo operation for removing a perturbation term from the received signal d ⁇ u after the channel equalization.
- the modulo operation is signal processing given by equation (8).
- the modulo operation In the modulo operation, the magnitudes of the real part and the imaginary part of the output are larger than ⁇ and smaller than ⁇ , respectively, with respect to the input. Therefore, when the residual IUI and noise power are sufficiently small, the modulo operation can remove perturbation terms in which the magnitudes of the real part and the imaginary part are 2 ⁇ or more, respectively.
- the channel equalization unit 57 outputs the signal after channel equalization and modulo calculation to the demapping unit 59.
- the terminal devices 2-1 to 2-4 extract transmission data addressed to the own device from radio resources used for transmission of transmission data addressed to the own device.
- the output of the reference signal separation unit 51-5 may be input to the demapping unit 59 first, and only the radio resource component corresponding to the own device may be input to the channel equalization unit 57.
- the output of the demapping unit 59 is then input to the data demodulating unit 61 and the channel decoding unit 63, where data demodulation and channel decoding are performed.
- the channel equalizer 57 may not perform the modulo operation.
- OFDM signal transmission is performed and precoding is performed for each subcarrier, but there is no limitation on the transmission scheme (or access scheme) and the precoding application unit.
- the present embodiment is also applicable when precoding is performed for each resource block in which a plurality of subcarriers are grouped.
- a single carrier-based access scheme for example, single carrier frequency division multiple access (SC- (FDMA) method.
- the first embodiment aims to suppress the residual IUI generated due to the time variation error among the elements constituting the feedback error.
- the feedback error includes a quantization error in addition to a time variation error.
- the second embodiment is directed to a transmission method that takes into account a residual IUI generated due to a quantization error.
- the main difference between the first embodiment and the second embodiment is that in FIG. 7, the propagation path estimation unit 73, the feedback information generation unit 75, the channel, etc. of the terminal devices 2-1 to 2-4 The signal processing is performed by the conversion unit 57 and the channel information acquisition unit 33 of the base station apparatus 1.
- FIG. 7 is a block diagram showing a device configuration of a terminal device according to the second embodiment of the present invention.
- the feedback information generation unit 75 has an output toward the propagation path estimation unit 73 in addition to having an output toward the terminal antenna unit 51.
- the configuration of the terminal antenna unit 51 is the same as that in FIG. below, the signal processing which concerns on the feedback of CSI among the signal processing which a terminal device performs is demonstrated.
- the propagation path estimation unit 73 performs propagation path estimation based on the input signal.
- CSI-RS is not transmitted on all subcarriers, there are subcarriers for which CSI cannot be estimated directly, but in the following, CSI of all subcarriers is estimated by appropriate interpolation. The description will be made assuming that The propagation path estimation unit 73 outputs the estimated h u (t 1 ) to the feedback information generation unit 75.
- the feedback information generation unit 75 quantizes the input h u (t 1 ) into information that can be notified to the base station apparatus 1. Incidentally, it is required that the amount of information required for the terminal devices 2-1 to 2-4 to notify the base station device 1 of the propagation path information is as small as possible. In order to suppress the amount of information related to feedback, it is conceivable that the terminal apparatuses 2-1 to 2-4 notify the base station apparatus 1 only of CSI of some subcarriers. In this case, base station apparatus 1 estimates the CSI of other subcarriers by some estimation method based on the CSI of some subcarriers notified from terminal apparatuses 2-1 to 2-4. Hereinafter, this estimation method is referred to as a base station CSI estimation method.
- the CSI of the u-th terminal device estimated by the base station device 1 based on the base station CSI estimation method is represented by hu and FB .
- H u (t 1) and h u of the terminal devices 2-1 to 2-4 were estimated error between FB is that the quantization error.
- the terminal devices 2-1 to 2-4 provide the base station device 1 with control information that specifies the base station CSI estimation method in addition to the propagation path information that is finally notified to the base station device 1. Notice.
- the control information specifying the base station CSI estimation method is not limited to anything. For example, it is conceivable to notify information specifying an interpolation method.
- Base station apparatus 1 can estimate CSI of other subcarriers by performing some interpolation based on the CSI of some subcarriers notified from terminal apparatuses 2-1 to 2-4. Therefore, if the terminal apparatuses 2-1 to 2-4 notify the base station apparatus 1 of the interpolation method and the base station apparatus 1 estimates the CSI based on the notified interpolation method, the terminal apparatuses 2-1 to 2-4 Can grasp hu and FB of all subcarriers.
- the terminal devices 2-1 to 2-4 calculate the most suitable interpolation method for estimating the CSI of other subcarriers from the CSI of some subcarriers notified to the base station device 1.
- the base station apparatus 1 may be controlled to notify the interpolation method.
- Various interpolation methods are conceivable, such as polynomial interpolation such as 0th order interpolation and 1st order interpolation, and sinc function interpolation. Therefore, the terminal apparatuses 2-1 to 2-4 know in advance the interpolation methods that can be executed by the base station apparatus 1, and the terminal apparatus 2-1 to 2-4 determines the most appropriate interpolation method among them. You may control to notify the station apparatus 1.
- the control information designating the base station CSI estimation method includes information designating the information amount compression technique.
- the terminal devices 2-1 to 2-4 do not have to notify control information for designating the base station CSI estimation method. Absent.
- the terminal devices 2-1 to 2-4 are configured to specify the base station CSI estimation method.
- the base station apparatus 1 may determine the base station CSI estimation method. In this case, the base station apparatus 1 notifies the terminal apparatuses 2-1 to 2-4 of control information that allows grasping which base station CSI estimation method is used.
- the feedback information generation unit 75 of the terminal devices 2-1 to 2-4 specifies the control information associated with the CSI notified to the base station device 1 and the base station CSI estimation method.
- the control information is also output to the radio transmission unit 51-2 of the terminal antenna unit 51.
- the feedback information generation unit 75 also calculates hu and FB and outputs them to the propagation path estimation unit 73.
- the wireless transmission unit 51-2 converts the input control information into a signal that can be transmitted to the base station apparatus 1, and then outputs the signal to the antenna 51-7.
- the configuration of the base station apparatus 1 according to the second embodiment is the same as that of FIG. 2 and FIG. 3, and is different from the first embodiment in the signal processing performed by the propagation path information acquisition unit 33.
- the signal processing in the propagation path information acquisition unit 33 will be described.
- the propagation path information acquisition unit 33 based on the control information input from the control information acquisition unit 31 and associated with the propagation path information between the terminal devices 2-1 to 2-4, the propagation path of all subcarriers Information hu and FB are calculated.
- the base station apparatus 1 is based on the base station CSI estimation method specified by the control information specifying the base station CSI estimation method notified from the terminal apparatuses 2-1 to 2-4.
- the channel information hu and FB of all subcarriers are calculated from the control information associated with the channel information between 2 and 4, and output to the precoding unit 27.
- the precoding unit 27 performs precoding based on the input propagation path information hu and FB . Since the signal processing in the other constituent devices of the base station device 1 is the same as that in the first embodiment, the description thereof is omitted.
- the propagation path information estimated at time t 1 h u (t 1) to be notified from the base station apparatus 1 a w u multiplied by the h u (t 1 ) W u was output to the channel equalization unit 57 as information used for channel equalization.
- the propagation path information h u (t 1 ) estimated at time t 1 instead of the propagation path information h u (t 1 ) estimated at time t 1 , w notified from the base station apparatus 1 to h u and FB input from the feedback information generation unit 75.
- h u and FB w u multiplied by u are output to the channel equalization unit 57 as information used for channel equalization.
- the channel equalization unit 57 suppresses the residual IUI generated due to the feedback error by performing channel equalization by dividing Equation (9) by hu and FB w u as in the first embodiment. It becomes possible to do.
- the error vectors eu and FB include an error between the propagation path information at time t 1 and the propagation path information at time t 2 , according to the method of the present embodiment, the time variation of the propagation path. It is possible to suppress the residual IUI generated due to the above.
- the signal processing in the second embodiment is all the same as that in the first embodiment. Therefore, the method of the first embodiment and the method of the second embodiment may be controlled so as to be switched according to the magnitude of the quantization error.
- the second embodiment is directed to MU-MIMO transmission based on nonlinear precoding in an environment where quantization errors caused by CSI quantization cannot be ignored. According to the second embodiment, the residual IUI generated due to the quantization error can be suppressed, so that excellent transmission characteristics can be realized.
- a wireless communication system that uses FDD that uses different carrier frequencies for uplink transmission and downlink transmission as a duplex system is targeted.
- the third embodiment is directed to a wireless communication system that uses time division duplex (TDD) that uses the same carrier frequency for uplink transmission and downlink transmission as a duplex scheme.
- TDD time division duplex
- FIG. 8 is a diagram illustrating an example of a frame format according to the third embodiment.
- an uplink signal ('U' in FIG. 8) and a downlink signal ('D' in FIG. 8) are alternately transmitted.
- Allocation of uplink and downlink radio resources may be equally distributed or biased.
- U terminal apparatuses are connected to the base station apparatus at the same time, and the allocated radio resources are the same in the uplink and downlink.
- a case where MU-MIMO transmission is performed in uplink / downlink transmission is targeted.
- this embodiment includes a case where different radio resources are allocated in uplink and downlink transmissions and a case where MU-MIMO transmission is not performed in uplink transmissions.
- the description will focus on downlink transmission that performs MU-MIMO transmission based on nonlinear precoding.
- the transmission method in uplink transmission is not limited to anything.
- OFDM signal transmission targeted for downlink transmission of the first and second embodiments may be used, or a single carrier access method such as SC-FDMA may be used.
- SC-FDMA single carrier access method
- the reference signals included in the uplink transmission signals from the terminal apparatuses 2-1 to 2-4 are orthogonal or pseudo-orthogonal between the terminal apparatuses. That is, it is assumed that the base station apparatus can estimate CSI between the terminal apparatuses 2-1 to 2-4 that are simultaneously connected from the reference signal included in the uplink signal.
- the base station apparatus estimates the CSI from the reference signal included in the uplink signals transmitted from the respective terminal devices 2-1 to 2-4 at time t 1.
- the base station apparatus based on the estimated CSI, and transmits the time t 2 to the respective terminal devices 2-1 to 2-4 addressed given that performing nonlinear precoding for downlink signals.
- FIG. 9 is a block diagram showing the configuration of the base station apparatus 1-1 according to the third embodiment of the present invention. However, only the configuration apparatus related to downlink signal transmission is shown.
- the base station apparatus 1-1 includes a channel coding unit 91, a data modulation unit 93, a mapping unit 95, a precoding unit 27, an antenna unit 29, a reference signal separation unit 101, A propagation path estimation unit (estimation unit) 103 and a control information generation unit 105 are included.
- Precoding unit 27 is the number of subcarriers N c
- the antenna unit 29 is present respectively by the number of transmit antennas N t.
- the configuration of the antenna unit 29 is the same as that shown in FIG. However, the output of the wireless reception unit 29-4 is input to the reference signal separation unit 101, not the control information acquisition unit 31.
- the antenna of the antenna unit 29 receives signals transmitted from the terminal devices 2-1 to 2-4 at the time t1, and inputs the signals to the radio reception unit 29-4.
- the radio reception unit 29-4 converts the input signal into a baseband signal and then outputs the signal to the reference signal separation unit 101.
- the output of the radio reception unit 29-4 is directly input to the reference signal separation unit 101.
- the actual uplink signal includes not only the reference signal but also a data signal and other signals.
- the control signal is also included.
- the output from the radio receiving unit 29-4 is processed by the GI removing unit 51-3, the FFT unit 51-4, etc. Input to the unit 101.
- the signal processing to be performed on the received signal before being input to the reference signal separation unit 101 is determined depending on the transmission scheme of uplink transmission.
- the reference signal separation unit 101 separates a reference signal for estimating CSI between the base station apparatus 1-1 and each terminal apparatus at time t 1 from the input signal, and outputs the reference signal to the propagation path estimation unit 103 To do.
- channel estimation unit 103 based on the input reference signal, the CSI between the base station apparatus 11 each terminal estimates at time t 1, the output to the precoding unit 27.
- the configuration of the precoding unit 27 is the same as that shown in FIG. However, what is output to the control information generation unit 105, in addition to the linear filter w u generated by the linear filter generation unit 27-1, the uplink any time CSI input to the precoding unit 27 Information indicating whether the signal is based on the signal is also included. In addition, about the time to notify, you may notify separately for every terminal device, and you may control to notify an average value.
- FIG. 10 is a block diagram showing a configuration of a terminal apparatus according to the third embodiment of the present invention.
- the terminal device 20 includes a terminal antenna unit 51, a propagation path estimation unit 112, a channel equalization unit 114, a demapping unit 116, a data demodulation unit 118, a channel decoding unit 120, And a link signal generator 122.
- the uplink signal generation unit 122 will be described. As described in the description of the base station apparatus 1-1, in the present embodiment, the uplink transmission scheme is not limited to anything. However, the reference signal included in the uplink signal needs to be orthogonal or pseudo-orthogonal between the terminal devices 20 that are simultaneously connected. Therefore, the uplink signal generation unit 122 generates a signal including a reference signal in which orthogonality is maintained between the terminal devices 20. In order to maintain the orthogonality between the terminal apparatuses 20, the base station apparatus 1-1 may be controlled to notify the radio resource for transmitting the reference signal, or the predetermined radio resource may always be used. You may control. The signal generated by the uplink signal generation unit 122 is output toward the terminal antenna unit 51.
- the configuration of the terminal antenna unit 51 is the same as that shown in FIG. However, the output of the uplink signal generation unit 122 is input to the wireless transmission unit 51-2. Radio transmission section 51-2 converts the input signal into a signal that can be transmitted to base station apparatus 1-1, and then outputs the signal to antenna 51-7. The antenna 51-7 transmits the input signal to the base station apparatus 1-1.
- a signal transmitted from the antenna at time t 1 receives the base station apparatus 11, based on the reference signal included in the received signal, the channel estimation unit of the base station apparatus 1-1 103 will estimate the CSI at time t 1 .
- the control information acquisition unit 51-6 includes the linear filter w u generated by the linear filter generation unit 27-1 of the base station apparatus 1-1 and generated by the control information generation unit 105 of the base station apparatus 1-1. Associated control information is input. Also, the control information acquisition unit 51-6 determines at which time the uplink signal the reference signal used for CSI estimation input to the precoding unit 27 of the base station apparatus 1-1 was included. The control information shown is also input. Based on the two pieces of input control information, the control information acquisition unit 51-6 estimates the linear filter w u and time t 1 and outputs them to the propagation path estimation unit 112.
- propagation path estimation section 112 estimates and stores CSI with base station apparatus 1-1 based on CSI-RS. Note that the propagation path estimation unit 112 also needs to store CSI estimated based on CSI-RS included in downlink signals received at other times.
- the channel equalization unit 114 determines the channel based on the CSI estimated by the CSI-RS, the information about the linear filter w u notified from the base station apparatus 1-1, and the time t 1. Propagation path information required for equalization is estimated.
- the propagation path estimation unit 112 uses the CSI estimated by the CSI-RS included in the downlink signal closest to the time t 1 notified from the base station apparatus 1-1 as a base station.
- the value obtained by multiplying the notified from 1-1 linear filter w u, is output toward the channel equalizer 114 as channel estimation values.
- the terminal device 20 uses the CSI estimated based on the CSI-RS included in the downlink signal received immediately before time t 1.
- a value obtained by multiplying w u is output to the channel equalization unit 114.
- the terminal device 20 based on the time nearest the CSI at time t 1, by performing a channel equalization, as in the first and second embodiments, it is possible to minimize the residual IUI Become.
- the propagation path estimation unit 112 may estimate the propagation path information at time t 1 based on a plurality of propagation path information estimated by the propagation path estimation unit 112 based on the CSI-RS in the past from time t 2. . In this case, it may be estimated based on simple polynomial interpolation, or may be estimated based on a least square criterion or a mean square error minimum criterion.
- a communication system using TDD as a duplex system is targeted. According to the present embodiment, even in a communication system using TDD, it is possible to suppress the influence of the residual IUI that occurs due to the time fluctuation of the propagation path, so that the transmission characteristics of nonlinear MU-MIMO transmission can be improved. Is possible.
- the terminal apparatus is a terminal apparatus that receives a radio signal that has been subjected to nonlinear precoding and spatially multiplexed from a base station apparatus that includes a plurality of antennas, and a propagation path between the base station apparatus and the base station apparatus
- a channel estimation unit that estimates information, a control information acquisition unit that acquires a linear filter calculated by the base station device, and the radio signal received at a first time, than the first time.
- a channel equalization unit that performs channel equalization processing based on the propagation path information at the second time in the past and the linear filter.
- channel equalization processing is performed on the radio signal received at the first time based on the propagation path information and the linear filter at the second time prior to the first time. It is possible to suppress the residual IUI generated due to the time fluctuation of the propagation path. As a result, transmission can be performed without causing significant deterioration in transmission characteristics even in an environment where the time variation of the propagation path cannot be ignored.
- the terminal device of this embodiment includes a feedback information generation unit that generates feedback information including propagation path information at the second time, and a wireless transmission unit that notifies the base station device of the feedback information.
- the base station apparatus since feedback information including propagation path information at the second time is generated and the feedback information is notified to the base station apparatus, the base station apparatus performs nonlinear processing based on the propagation path information at the second time. Precoding is performed, and in the terminal device, for the radio signal received at the first time, the channel is determined based on the propagation path information at the second time past the first time and the linear filter. By performing the equalization process, it is possible to perform a process for suppressing the residual IUI generated due to the time variation of the propagation path.
- the wireless transmission unit transmits a reference signal to the base station device.
- the reference signal is transmitted to the base station apparatus, it becomes possible to estimate the propagation path information in the base station apparatus.
- the channel equalization unit obtains from a channel gain at a second time with the base station device and a linear filter calculated by the base station device.
- the channel equalization processing is performed on the received radio signal at a first time based on the estimated propagation path value.
- the reception at the first time based on the propagation path estimated value obtained from the propagation path gain at the second time with the base station apparatus and the linear filter calculated by the base station apparatus Since the channel equalization process is performed on the wireless signal, the residual IUI generated due to the time variation of the propagation path can be suppressed.
- the linear filter is calculated based on propagation path information at the second time.
- the base station apparatus since the linear filter is calculated based on the propagation path information at the second time, the base station apparatus performs nonlinear precoding based on the propagation path information at the second time.
- the terminal device performs channel equalization processing on the radio signal received at the first time based on the propagation path information at the second time past the first time and the linear filter. As a result, it is possible to perform processing for suppressing the residual IUI generated due to the time fluctuation of the propagation path.
- the terminal apparatus is a terminal apparatus that receives a radio signal that has been subjected to nonlinear precoding and spatially multiplexed from a base station apparatus that includes a plurality of antennas.
- a channel estimation unit that estimates channel information
- a control information acquisition unit that acquires a linear filter calculated by the base station device, and a radio signal received from the base station device
- a channel equalization unit that performs channel equalization processing based on the same propagation path information as the propagation path information used for the calculation of the linear filter and the linear filter.
- channel equalization is performed on the radio signal received from the base station apparatus based on the same propagation path information and the linear filter as the propagation path information used for calculating the linear filter in the base station apparatus. Since the processing is performed, it is possible to suppress the residual IUI that occurs due to the time fluctuation of the propagation path. As a result, transmission can be performed without causing significant deterioration in transmission characteristics even in an environment where the time variation of the propagation path cannot be ignored.
- the base station apparatus includes a plurality of antennas, and a non-linear precoding and spatially multiplexed radio signal described in any of (1) to (6) above at a first time
- a base station apparatus that transmits to a plurality of terminal apparatuses, wherein nonlinear precoding is performed on a signal transmitted to each terminal apparatus based on propagation path information at a second time that is past the first time.
- control information including information indicating a linear filter is obtained by performing nonlinear precoding on a signal to be transmitted to each terminal device based on propagation path information at a second time that is past the first time. Since the wireless signal and the control information are generated and transmitted to each terminal device, the terminal device is configured to transmit the wireless signal received at the first time to the past of the first time.
- the base station apparatus of this embodiment acquires the feedback information including the propagation path information at the second time, and the propagation for acquiring the propagation path information at the second time from the feedback information.
- a non-linear precoding unit that performs non-linear precoding on a signal to be transmitted to each terminal device based on propagation path information at the second time.
- the feedback information including the propagation path information at the second time is obtained, the propagation path information at the second time is obtained from the feedback information, and the propagation path information at the second time is obtained. Since the signal transmitted to each terminal apparatus is subjected to non-linear precoding, the terminal apparatus propagates the radio signal received at the first time at a second time that is earlier than the first time. By performing channel equalization processing based on the path information and the linear filter, it is possible to perform processing for suppressing the residual IUI generated due to time fluctuation of the propagation path.
- the base station apparatus of the present embodiment includes a receiving unit that receives a radio signal including a reference signal from the terminal apparatus at the second time, and a reference that separates the reference signal from the received radio signal.
- the terminal device since the signal to be transmitted to the terminal device is subjected to nonlinear precoding based on the propagation path information with the terminal device at the second time, the terminal device receives the signal at the first time.
- channel equalization processing By performing channel equalization processing on the wireless signal based on the propagation path information and the linear filter at a second time that is past the first time, due to the time variation of the propagation path It is possible to perform processing for suppressing the generated residual IUI.
- the wireless communication system includes the terminal device described in (1) above and the base station device described in (7) above.
- channel equalization processing is performed on the radio signal received at the first time based on the propagation path information and the linear filter at the second time prior to the first time. It is possible to suppress the residual IUI generated due to the time fluctuation of the propagation path. As a result, even in an environment where the time variation of the propagation path cannot be ignored, transmission can be performed without causing a large deterioration in transmission characteristics.
- the reception method of the present embodiment is a reception method for a terminal device that receives a radio signal that is subjected to nonlinear precoding and spatially multiplexed from a base station device including a plurality of antennas. Estimating the propagation path information between the base station apparatus, obtaining the linear filter calculated by the base station apparatus, and the radio signal received at the first time from the first time. And a step of performing channel equalization processing based on the propagation path information at the past second time and the linear filter.
- channel equalization processing is performed on the radio signal received at the first time based on the propagation path information and the linear filter at the second time prior to the first time. It is possible to suppress the residual IUI generated due to the time fluctuation of the propagation path. As a result, transmission can be performed without causing significant deterioration in transmission characteristics even in an environment where the time variation of the propagation path cannot be ignored.
- the integrated circuit of the present embodiment is an integrated circuit that is mounted on a terminal device to cause the terminal device to exhibit a plurality of functions, and includes non-linear precoding from a base station device including a plurality of antennas.
- channel equalization processing is performed on the radio signal received at the first time based on the propagation path information and the linear filter at the second time prior to the first time. It is possible to suppress the residual IUI generated due to the time fluctuation of the propagation path. As a result, transmission can be performed without causing significant deterioration in transmission characteristics even in an environment where the time variation of the propagation path cannot be ignored.
- the terminal device 2 and the terminal device 20 of the present invention are not limited to application to mobile station devices such as cellular systems, but are stationary or non-movable electronic devices installed indoors and outdoors, such as AV Needless to say, the present invention can be applied to equipment, kitchen equipment, cleaning / washing equipment, air conditioning equipment, office equipment, vending machines, and other daily life equipment.
- the program that operates in the mobile station apparatus and the base station apparatus related to the present invention is a program (a program that causes a computer to function) that controls the CPU and the like so as to realize the functions of the above-described embodiments related to the present invention.
- Information handled by these devices is temporarily stored in the RAM at the time of processing, then stored in various ROMs and HDDs, read out by the CPU, and corrected and written as necessary.
- a recording medium for storing the program a semiconductor medium (for example, ROM, nonvolatile memory card, etc.), an optical recording medium (for example, DVD, MO, MD, CD, BD, etc.), a magnetic recording medium (for example, magnetic tape, Any of a flexible disk etc. may be sufficient.
- the processing is performed in cooperation with the operating system or other application programs.
- the functions of the invention may be realized.
- the program when distributing to the market, can be stored and distributed on a portable recording medium, or transferred to a server computer connected via a network such as the Internet.
- the storage device of the server computer is also included in the present invention.
- part or all of the mobile station apparatus and the base station apparatus in the above-described embodiment may be realized as an LSI that is typically an integrated circuit.
- Each functional block of the mobile station apparatus and the base station apparatus may be individually made into a processor, or a part or all of them may be integrated into a processor.
- the method of circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor.
- an integrated circuit based on the technology can also be used.
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Abstract
Description
セルラーシステムや無線LANシステムなどで実用化されている。MIMO技術による周波数利用効率改善量は送受信アンテナ数に比例する。しかし、端末装置に配置できる受信アンテナ数には限りがある。そこで、同時接続する複数端末装置を仮想的な大規模アンテナアレーとみなし、基地局装置から各端末装置への送信信号を空間多重させるマルチユーザMIMO(Multi User-MIMO(MU-MIMO))が周波数利用効率の改善に有効である。
ている。
図1は、本発明の第1の実施形態に係る無線通信システムの概略を示す図である。第1の実施形態においては、Nt本の送信アンテナを有し、非線形プリコーディングが可能な基地局装置1(無線送信装置とも呼ぶ)に対して、Nr本の受信アンテナを有する端末装置2(無線受信装置とも呼ぶ。図1では、端末装置2-1~2-4を示す。以下、これらを合わせて端末装置とも表す)がU個接続しているMU-MIMO伝送を対象とする。各端末装置2-1~2-4にはそれぞれL個のデータを同時に送信するものとし(同時送信するデータ数のことをランク数とも呼ぶ)、U×L=NtおよびL=Nrであるものとする。
図2は、本発明の第1の実施形態に係る基地局装置の構成を示すブロック図である。図2に示すように、基地局装置1は、チャネル符号化部21と、データ変調部23と、マッピング部25と、プリコーディング部(非線形プリコーディング部)27と、アンテナ部29と、制御情報取得部31と、伝搬路情報取得部33と、制御情報生成部35とを含んで構成されている。プリコーディング部27はサブキャリア数Nc、アンテナ部29は送信アンテナ数Ntだけそれぞれ存在する。
図5は、本発明の第1の実施形態に係る端末装置の構成を示すブロック図である。図5に示すように、端末装置は端末アンテナ部51と、伝搬路推定部53と、フィードバック情報生成部55と、チャネル等化部57と、デマッピング部59とデータ復調部61と、チャネル復号部63とを含んで構成されている。そのうち、端末アンテナ部51は受信アンテナ数Nrだけ存在する。ただし、以下の説明では、受信アンテナ数はNr=1であるものとして説明を行なう。また、時刻t2において、基地局装置1より送信された信号を受信したものとして説明を行なう。
第1の実施形態においては、フィードバック誤差を構成する要素の中で、時変動誤差に起因して発生する残留IUIを抑圧することを目的としていた。しかし、フィードバック誤差には時変動誤差に加えて、量子化誤差も含まれる。第2の実施形態では、量子化誤差に起因して発生する残留IUIも考慮にいれた伝送方式を対象とする。第1の実施形態と、第2の実施形態との間の主な違いは、図7において、端末装置2-1~2-4の伝搬路推定部73と、フィードバック情報生成部75とチャネル等化部57と、基地局装置1の伝搬路情報取得部33における信号処理にある。
図7は、本発明の第2の実施形態に係る端末装置の装置構成を示すブロック図である。装置構成は図5とほぼ同様であるが、フィードバック情報生成部75は端末アンテナ部51に向けた出力を持つことに加えて、伝搬路推定部73に向けた出力も有する。なお、端末アンテナ部51の構成は図6と同じである。以下では、端末装置が行なう信号処理のうち、CSIのフィードバックに係る信号処理について説明する。
第2の実施形態に係る基地局装置1の構成は図2および図3と同様であり、第1の実施形態と異なるのは、伝搬路情報取得部33で行なわれる信号処理にある。そこで、以下では、伝搬路情報取得部33における信号処理について説明する。
以下では、時刻t2に受信された信号に対する端末装置2-1~2-4の信号処理について説明を行なう。第1の実施形態と信号処理が異なるのは、伝搬路推定部73における信号処理である。
第1および第2の実施形態では、上りリンク伝送と、下りリンク伝送とで、異なる搬送周波数を用いるFDDを複信方式として用いる無線通信システムを対象とした。第3の実施形態では、上りリンク伝送と、下りリンク伝送とで同じ搬送波周波数を用いる時間分割複信(Time Division Duplex(TDD))を複信方式として用いる無線通信システムを対象とする。
図9は、本発明の第3の実施形態に係る基地局装置1-1の構成を示すブロック図である。ただし、下りリンク信号伝送に関連する構成装置についてのみ示している。図9に示すように、基地局装置1-1は、チャネル符号化部91と、データ変調部93と、マッピング部95と、プリコーディング部27と、アンテナ部29と、参照信号分離部101と、伝搬路推定部(推定部)103と、制御情報生成部105とを含んで構成されている。プリコーディング部27はサブキャリア数Nc、アンテナ部29は送信アンテナ数Ntだけそれぞれ存在する。アンテナ部29の構成は図4と同様である。ただし、無線受信部29-4の出力は、制御情報取得部31ではなく、参照信号分離部101に入力されることになる。
図10は、本発明の第3の実施形態に係る端末装置の構成を示すブロック図である。図10に示すように、端末装置20は端末アンテナ部51と、伝搬路推定部112と、チャネル等化部114と、デマッピング部116と、データ復調部118と、チャネル復号部120と、上りリンク信号生成部122とを含んで構成されている。そのうち、端末アンテナ部51は受信アンテナ数Nrだけ存在する。ただし、以下の説明では、受信アンテナ数はNr=1であるものとして説明を行なう。
以上、この発明の実施形態について図面を参照して詳述してきたが、具体的な構成はこの実施形態に限られるものではなく、この発明の要旨を逸脱しない範囲の設計等も特許請求の範囲に含まれる。
2-1~2-4、20 端末装置
21 チャネル符号化部
23 データ変調部
25 マッピング部
27 プリコーディング部
27-1 線形フィルタ生成部
27-2 摂動ベクトル探査部
27-3 送信信号生成部
29 アンテナ部
29-1 IFFT部
29-2 GI挿入部
29-3 無線送信部
29-4 無線受信部
29-5 アンテナ
31 制御情報取得部
33 伝搬路情報取得部
35 制御情報生成部
51 端末アンテナ部
51-1 無線受信部
51-2 無線送信部
51-3 GI除去部
51-4 FFT部
51-5 参照信号分離部
51-6 制御情報取得部
51-7 アンテナ
53 伝搬路推定部
55 フィードバック情報生成部
57 チャネル等化部
59 デマッピング部
61 データ復調部
63 チャネル復号部
73 伝搬路推定部
75 フィードバック情報生成部
91 チャネル符号化部
93 データ変調部
95 マッピング部
101 参照信号分離部
103 伝搬路推定部
105 制御情報生成部
112 伝搬路推定部
114 チャネル等化部
116 デマッピング部
118 データ復調部
120 チャネル復号部
122 上りリンク信号生成部
Claims (12)
- 複数のアンテナを備える基地局装置から非線形プリコーディングが施され空間多重された無線信号を受信する端末装置であって、
前記基地局装置との間の伝搬路情報を推定する伝搬路推定部と、
前記基地局装置で算出された線形フィルタを取得する制御情報取得部と、
第1の時刻で受信した前記無線信号に対して、前記第1の時刻よりも過去の第2の時刻における伝搬路情報および前記線形フィルタに基づいて、チャネル等化処理を行なうチャネル等化部と、を備えることを特徴とする端末装置。 - 前記第2の時刻における伝搬路情報を含むフィードバック情報を生成するフィードバック情報生成部と、
前記フィードバック情報を前記基地局装置へ通知する無線送信部と、を更に備えることを特徴とする請求項1記載の端末装置。 - 前記無線送信部は、前記基地局装置に対して参照信号を送信することを特徴とする請求項2記載の端末装置。
- 前記チャネル等化部は、前記基地局装置との間の第2の時刻における伝搬路利得と前記基地局装置で算出された線形フィルタとから求められる伝搬路推定値に基づいて、第1の時刻で前記受信した無線信号に対してチャネル等化処理を行なうことを特徴とする請求項2に記載の端末装置。
- 前記線形フィルタは、前記第2の時刻における伝搬路情報に基づいて算出されたことを特徴とする請求項2に記載の端末装置。
- 複数のアンテナを備える基地局装置から非線形プリコーディングが施され空間多重された無線信号を受信する端末装置であって、
前記基地局装置との間の伝搬路情報を推定する伝搬路推定部と、
前記基地局装置で算出された線形フィルタを取得する制御情報取得部と、
前記基地局装置から受信した無線信号に対して、前記基地局装置で線形フィルタの算出に用いられた伝搬路情報と同一の伝搬路情報および前記線形フィルタに基づいて、チャネル等化処理を行なうチャネル等化部と、を備えることを特徴とする端末装置。 - 複数のアンテナを備え、非線形プリコーディングを施し空間多重した無線信号を第1の時刻に請求項1から請求項3のいずれかに記載の複数の端末装置に対して送信する基地局装置であって、
前記第1の時刻よりも過去の第2の時刻における伝搬路情報に基づいて、前記各端末装置に送信する信号に非線形プリコーディングを施す非線形プリコーディング部と、
線形フィルタを示す情報を含む制御情報を生成する制御情報生成部と、
前記無線信号および前記制御情報を前記各端末装置に対して送信する送信部と、を備えることを特徴とする基地局装置。 - 前記第2の時刻における伝搬路情報を含むフィードバック情報を取得する取得部と、
前記フィードバック情報から前記第2の時刻における伝搬路情報を取得する伝搬路情報取得部と、を更に備え、
前記非線形プリコーディング部は、前記第2の時刻における伝搬路情報に基づいて、前記各端末装置に送信する信号に非線形プリコーディングを施すことを特徴とする請求項7記載の基地局装置。 - 前記第2の時刻において、前記端末装置から参照信号を含む無線信号を受信する受信部と、
前記受信した無線信号から参照信号を分離する参照信号分離部と、
前記参照信号に基づいて、前記第2の時刻における前記端末装置との間の伝搬路情報を推定する推定部と、を備え、
前記非線形プリコーディング部は、前記第2の時刻における前記端末装置との間の伝搬路情報に基づいて、前記端末装置へ送信する信号に非線形プリコーディングを施すことを特徴とする請求項7記載の基地局装置。 - 請求項1記載の端末装置と、請求項7記載の基地局装置と、から構成されることを特徴とする無線通信システム。
- 複数のアンテナを備える基地局装置から非線形プリコーディングが施され空間多重された無線信号を受信する端末装置の受信方法であって、
前記基地局装置との間の伝搬路情報を推定するステップと、
前記基地局装置で算出された線形フィルタを取得するステップと、
第1の時刻で受信した前記無線信号に対して、前記第1の時刻よりも過去の第2の時刻における伝搬路情報および前記線形フィルタに基づいて、チャネル等化処理を行なうステップと、を少なくとも含むことを特徴とする受信方法。 - 端末装置に実装されることによって、前記端末装置に複数の機能を発揮させる集積回路であって、
複数のアンテナを備える基地局装置から非線形プリコーディングが施され空間多重された無線信号を受信する機能と、
前記基地局装置との間の伝搬路情報を推定する機能と、
前記基地局装置で算出された線形フィルタを取得する機能と、
第1の時刻で受信した前記無線信号に対して、前記第1の時刻よりも過去の第2の時刻における伝搬路情報および前記線形フィルタに基づいて、チャネル等化処理を行なう機能と、の一連の機能を前記端末装置に発揮させることを特徴とする集積回路。
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