JP5789607B2 - Communication apparatus and communication system - Google Patents

Description

  The present invention relates to a communication system and a communication apparatus that transmit and receive interference with signal processing suppressed in advance.

  MIMO (Multiple-Input Multiple-Output) transmission technology that uses multiple antennas for transmission and reception, spatially multiplexes multiple different data sequences (data streams) in the same frequency band and communicates simultaneously, It has been put to practical use in wireless LANs and cellular systems.

  In a next-generation cellular system or the like, a system has been proposed in which the number of transmission antennas included in a base station apparatus (transmission apparatus) is significantly larger than the number of reception antennas included in a terminal apparatus (reception apparatus). In such a system, in order to further improve the system throughput by effectively using the transmission antenna of the base station apparatus, multi-user MIMO (Multi-User MIMO) that multiplexes data sequences addressed to a plurality of terminal apparatuses (users) ) Has been proposed.

  However, since signals received by other terminals cannot be known between a plurality of terminal devices that receive signals multiplexed in multi-user MIMO, inter-user interference (Multi -User Interference (MUI) significantly deteriorates the characteristics.

  Here, if the base station apparatus knows CSI (Channel State Information) that is channel state information from each transmitting antenna of the base station apparatus to each receiving antenna of each terminal apparatus, it does not impose a heavy load on the terminal apparatus. Several methods have been proposed that can generate a transmission signal that can suppress MUI at the time of reception in a terminal device (Non-Patent Document 1).

  For example, there is a method of performing transmission after precoding the transmission signal in the base station apparatus so that it can be received in a state in which the MUI is suppressed at the time of reception in the terminal apparatus.

As an example, an inverse matrix H ⁻¹ (or a pseudo inverse matrix H ^† =) is obtained from a channel matrix H having a complex propagation path gain between each transmission antenna obtained from CSI and each reception antenna of each terminal device as an element. H ^H (HH ^H ) ⁻¹ : The superscript H represents Hermitian conjugate) is used as a weighting matrix (linear filter) W to weight the transmission signal (multiply the transmission signal by W = H ⁻¹ ) Zero -Forcing (ZF) precoding and weight matrix (linear filter) W = H ^H (HH ^H + αI) ⁻¹ (I is a unit matrix, α is a minimum mean square error (MMSE) standard) There is linear precoding (beamforming) for precoding the transmission signal by linear processing, such as MMSE precoding that weights the transmission signal with a normalization factor).

  As another example, the transmission power is reduced in the signal space in order to subtract the interference signal component obtained from the CSI from the transmission signal in advance and suppress the transmission power that increases after the interference subtraction. There is nonlinear precoding, in which a transmission signal is precoded by nonlinear processing that encodes a signal after interference subtraction at a signal point.

  As one of the nonlinear precodings, Tomlinson-Harashima precoding (Tomlinson-Harashima precoding) that can suppress an increase in transmission power by performing a modulo operation on a signal in both transmitting and receiving apparatuses. Precoding (THP) has been proposed (Non-Patent Document 2, Non-Patent Document 3, Non-Patent Document 4). At this time, the terminal device on the receiving side also performs a remainder calculation similar to transmission on the received signal.

  Furthermore, considering the characteristic degradation called Modulo-Loss at low signal-to-noise power ratio (SNR) caused by the residue calculation in THP, the MUI is small and the transmission power suppression effect by the residue operation is small. A method in which the same processing as linear precoding is performed on a terminal without applying a residue calculation, and a non-linear precoding by THP is applied only to a terminal having a large MUI and a large transmission power suppression effect by the residue operation. Has been proposed (Non-Patent Document 5).

  Further, in Non-Patent Document 6, in consideration that the signal point arrangement at the time of modulation in the base station apparatus is repeated with a modulo width, it is repeated with a received signal point (with noise added) and a modulo width. A method of calculating a log likelihood ratio (Log Likelihood Ratio: LLR) of demodulated bits from the Euclidean distance from each candidate signal point is described (demodulation processing by soft decision).

Spencer et al., "An Introduction to the Multi-User MIMO Downlink", IEEE Communication Magazine, Vol. 42, Issue 10, p. 60-67, October 2004 Harashima et al., "Matched-Transmission Technique for Channels With Intersymbol Interference", IEEE Transaction on Communications, Vol.COM-20, No.4, p.774-780, August 1972 J. Liu et al., “Improved Tomlinson-Harashima Precoding for the Downlink of Multiple Antenna Multi-User Systems”, Proc. IEEE Wireless and Communications and Networking Conference, p.466-472, March 2005. M. Joham et al., “MMSE Approaches to Multiuser Spatio-Temporal Tomlinson-Harashima Precoding”, Proc. 5th Int. ITG Conf. On Source and Channel Coding, p.387-394, January 2004 Nakano et al., “Proposal for Downlink MU-MIMO THP to Adaptively Control Transmission Methods”, IEICE Technical Report, RCS2009-293, March 2010 Kazuki Takeda et al., “Single-Carrier HARQ Using Joint THP and FDE”, Proc. 2007 IEEE 66th Vehicular Technology Conference (VTC-2007 Fall), p.1188-1192, September 2007

  Unlike a case of linear precoding, a communication apparatus that receives a signal transmitted with interference suppressed by THP (nonlinear precoding) needs to perform a remainder calculation similar to that on the transmission side.

  For this reason, in a communication system, when a transmission apparatus (base station apparatus) that performs interference suppression by linear precoding and a transmission apparatus that performs interference suppression by THP coexist, or when the transmission apparatus uses interference suppression and THP by linear precoding. When dealing with both types of interference suppression, as in Non-Patent Document 5, two types of interference suppression methods are used, such as when the transmission apparatus performs interference suppression by combining linear precoding and THP simultaneously. When used together, the receiving device (terminal device) needs to switch whether or not to perform remainder calculation according to the interference suppression method. For this reason, the transmission apparatus receives linear precoding for a reception apparatus (terminal apparatus) that receives a signal transmitted with interference suppression, and the signal received by the reception apparatus is not subjected to a residue calculation. Or THP (remainder operation is performed) must be notified by control information or the like.

  An object of the present invention is to allow a receiving device to determine whether or not there is a remainder operation without notification from a transmitting device.

  According to one aspect of the present invention, there is provided a receiving apparatus that receives a signal that selectively or simultaneously used interference suppression by linear precoding and interference suppression by nonlinear precoding, and performs a remainder operation on a received signal. There is provided a receiving apparatus characterized by performing a remainder operation on a received signal when the determination result is a result of performing a remainder operation.

  Thereby, the presence or absence of the remainder calculation can be determined on the receiving device side without notification from the transmitting device.

  Further, the present invention is a receiving apparatus that receives a signal in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or used simultaneously, and a reception quality estimated from a received signal, A remainder calculation determination unit that determines whether or not to perform a remainder calculation on the received signal based on the distribution of the received signal measured from the received signal, and when the determination result is a remainder calculation. And a residue calculation unit that performs a residue calculation on the received signal.

  In addition, the present invention is a receiving apparatus that receives a signal in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or simultaneously used, and estimates reception quality of a received signal A propagation path estimator, a signal distribution estimator for estimating a distribution of received signal points when it is assumed that no remainder calculation is performed at the time of transmission based on the estimation result of the reception quality, and a signal point of the received signal A signal distribution measurement unit that measures the distribution, and a remainder calculation determination that compares the estimation result of the reception signal point distribution with the measurement result of the reception signal point distribution and determines whether or not to perform a remainder calculation on the reception signal And a residue calculation unit that performs a residue calculation on a received signal when the determination result is a residue calculation.

  The remainder calculation determination unit determines that the remainder calculation is not performed when the degree of coincidence between the estimation result of the reception signal point distribution and the distribution shape of the measurement result of the reception signal point distribution is high, and when the degree of coincidence is low It is determined that a remainder operation is performed.

  In addition, the remainder calculation determination unit is a ratio that is distributed outside the modulo width in the estimation result of the reception signal point distribution, and a ratio that is distributed outside the modulo width in the measurement result of the reception signal point distribution. Are substantially equal, it is determined that the remainder calculation is not performed, and when the ratio in the measurement result of the received signal point distribution is larger, it is determined that the remainder calculation is performed.

  In addition, the present invention is a receiving apparatus that receives a signal in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or simultaneously used, and estimates reception quality of a received signal A propagation path estimator, a signal variance estimator that estimates the variance of the distribution of received signal points when it is assumed that no residue calculation is performed at the time of transmission based on the estimation result of the reception quality, and Whether the signal variance measurement unit for measuring the variance of the signal point distribution compares the estimation result of the variance of the received signal point distribution with the measurement result of the variance of the received signal point distribution and performs a remainder operation on the received signal A remainder calculation determination unit that determines whether or not, and a residue calculation unit that performs a residue calculation on a received signal when the determination result is a residue calculation. It is a device.

  The remainder calculation determining unit determines that the remainder calculation is not performed when the estimation result of the variance of the received signal point distribution and the measurement result of the variance of the received signal point distribution are substantially equal, and the variance of the received signal point distribution If the measurement result is larger, it is determined that the remainder calculation is performed.

  In addition, the present invention is a receiving apparatus that receives a signal in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or simultaneously used, and estimates reception quality of a received signal The propagation path estimation unit and one or more subcarriers or frequency channels with good reception quality estimation results are selected, and the signal points of the received data symbols on the selected subcarriers or frequency channels are outside the modulo width. When it is located, it is determined that the remainder calculation is performed, and when it is located inside the modulo width, the remainder calculation determination unit that determines that the remainder calculation is not performed, and when the determination result is a residue calculation, And a remainder calculation unit that performs a remainder calculation on the received signal.

  In addition, the present invention is a transmission apparatus that transmits a signal by suppressing interference in a reception apparatus in advance by nonlinear precoding, and an interference component subtraction unit that subtracts an interference component from a modulation symbol, and the interference component is subtracted A remainder computation unit that performs a remainder operation on a modulation symbol; and a vector addition unit that adds an additional vector having a component that is an integral multiple of the modulo width of the remainder operation to a part of the symbols of the remainder operation result. It is a transmitter characterized by comprising. The positions of the partial symbols to which the additional vector is added are preferably determined in advance.

  In addition, the present invention is a receiving apparatus that receives a signal in which interference suppression by linear precoding and interference suppression by non-linear precoding are selectively used or used at the same time. If the signal point of the selected received data symbol is located outside the modulo width, it is determined that the remainder operation is performed, and if the signal point is located inside the modulo width, the remainder operation is performed. A reception device comprising: a remainder calculation determination unit that determines not to perform; and a residue calculation unit that performs a residue calculation on a received signal when the determination result is a residue calculation. is there.

  The present invention is also a communication system in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or used simultaneously, and interference in a receiving apparatus is suppressed in advance by signal processing. Performs a remainder operation on the received signal based on the transmitting device to transmit, the receiving unit that receives the transmitted signal, the reception quality estimated from the received signal, and the distribution of the received signal measured from the received signal A receiving device having a determination unit that determines whether or not and a residue calculation unit that performs a residue calculation on a received signal when the determination result is a residue calculation. is there.

  In addition, the present invention is a reception apparatus that receives a signal in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or simultaneously used, and performs a remainder operation from the received signal. In the receiving apparatus, the received signal is demodulated in consideration of signal point repetition by the remainder calculation when the determination result is a remainder calculation.

  Further, the present invention is a receiving apparatus that receives a signal in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or used simultaneously, and a reception quality estimated from a received signal, A remainder calculation determination unit that determines whether or not to perform a remainder calculation on the received signal based on the distribution of the received signal measured from the received signal, and when the determination result is a remainder calculation. And a demodulator that performs likelihood calculation in consideration of repetition of signal points by residue calculation from the received signal.

  In addition, the present invention is a receiving apparatus that receives a signal in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or simultaneously used, and estimates reception quality of a received signal The propagation path estimation unit and one or more subcarriers or frequency channels with good reception quality estimation results are selected, and the signal points of the received data symbols on the selected subcarriers or frequency channels are outside the modulo width. When it is located, it is determined that the remainder calculation is performed, and when it is located inside the modulo width, the remainder calculation determination unit that determines that the remainder calculation is not performed, and when the determination result is a residue calculation, And a demodulator that performs likelihood calculation in consideration of repetition of signal points by residue calculation from the received signal. A.

  According to another aspect of the present invention, there is provided a communication method in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or simultaneously used, and estimate reception quality of a received signal. A propagation path estimation step, a signal distribution estimation step for estimating a distribution of received signal points when it is assumed that no residue calculation is performed at the time of transmission based on the estimation result of the reception quality, and a signal point of the received signal A signal distribution measurement step for measuring a distribution, and a residue calculation determination for comparing whether the reception signal point distribution estimation result and the reception signal point distribution measurement result are compared, and determining whether or not to perform a residue calculation on the reception signal And a residue calculation step of performing a residue calculation on the received signal when the determination result is a residue calculation. Shin method is provided.

  The present invention may be a program for causing a computer to execute the communication method described above, or a computer-readable recording medium for recording the program.

  This specification includes the contents described in the specification and / or drawings of Japanese Patent Application No. 2010-173869, which is the basis of the priority of the present application.

  According to the present invention, in a communication system in which interference suppression by linear precoding and interference suppression by THP are selectively used or used at the same time, the presence / absence of a remainder calculation is notified without notification from the transmission device. Can be determined.

It is a figure which shows the example of schematic structure of the communication system in the 1st Embodiment of this invention. It is a block diagram which shows the structure of the base station apparatus in the 1st Embodiment of this invention. It is a block diagram which shows the example of 1 structure of the multiuser MIMO signal generation part 203a in the case of using linear precoding. It is a block diagram which shows the example of 1 structure of the multiuser MIMO signal generation part 203b in the case of using nonlinear precoding. It is a block diagram which shows the example of 1 structure of the multiuser MIMO signal generation part 203c in the case of using combining linear precoding and nonlinear precoding. It is a block diagram which shows the structure of the terminal device 600 in this Embodiment. It is a block diagram which shows the structure of the terminal device 600b in this Embodiment. The horizontal axis represents the in-phase component I-axis and the vertical axis represents the quadrature component Q-axis, showing the QPSK signal point arrangement diagram. It is a figure which shows received signal point arrangement | positioning in case a remainder calculation is performed in the base station apparatus (THP). It is the graph which calculated | required probability density distribution of the signal amplitude about the received signal point in SNR = infinity in the case where a remainder calculation is not performed in a base station apparatus (linear precoding) paying attention to an I axis (or Q axis). It is a graph of the result of having estimated the probability density distribution of the signal amplitude of the received signal when the received signal power is normalized to 1 at SNR = 3 dB using the equation (2). This is an example in which a signal amplitude distribution (frequency distribution, histogram) at the time of reception SNR = 3 dB when the remainder calculation is not performed in the base station apparatus (linear precoding) is obtained by computer simulation. It is an example which calculated | required the distribution (histogram) of the signal amplitude at the time of reception SNR = 3 dB in case a remainder calculation was performed in the base station apparatus (THP) by computer simulation. It is a block diagram which shows the structure of the terminal device in the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the terminal device in the 3rd Embodiment of this invention. It is a block diagram which shows one structural example of the multiuser MIMO signal generation part 203d in 4th Embodiment, when using combining linear precoding and nonlinear precoding. It is a conceptual diagram of the addition vector addition in the 3rd vector addition part and the 4th vector addition part. It is a figure which shows the example of a received signal point arrangement | positioning (when there is no noise) in the terminal device by which MUI was canceled by THP.

  Hereinafter, a communication technique according to an embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
For the communication technology according to the present embodiment, the base station device (transmitting device) performs multi-user MIMO transmission to four terminal devices from the first terminal device (receiving device) to the fourth terminal device, An example of a communication system in which inter-user interference (MUI) that occurs between streams addressed to a terminal device is suppressed in advance by linear precoding or non-linear precoding (THP) will be described.

  FIG. 1 is a diagram illustrating a schematic configuration example of a communication system according to the present embodiment. As shown in FIG. 1, in the communication system according to the present embodiment, base station apparatus 100 communicates with a plurality of terminal apparatuses (for example, first to fourth terminal apparatuses 101 to 104). In downlink transmission to a plurality of terminal apparatuses 101 to 104, the communication system performs multi-user MIMO transmission in which transmission data addressed to a plurality of terminal apparatuses is spatially multiplexed in the same frequency band and simultaneously communicated.

  Further, although a communication system using Orthogonal Frequency Division Multiplexing (OFDM) as a transmission method will be described as an example, the present invention is not limited to this.

  FIG. 2 is a functional block diagram showing a configuration example of the base station apparatus 100 in the present embodiment. The wireless reception unit 209 receives signals transmitted from the first terminal device 101, the second terminal device 102, the third terminal device 103, and the fourth terminal device 104 through the antenna unit 208 (208a to 208d). . The CSI acquisition unit 210 acquires CSI, which is channel state information transmitted from each terminal apparatus 101 to 104, from the received signal.

  The first to fourth encoding units 201a, 201b, 201c, and 201d are input with data sequences addressed to the first to fourth terminal apparatuses 101 to 104, respectively, and perform error correction encoding on each. Do.

  The first to fourth modulation units 202a, 202b, 202c, and 202d modulate the data sequences addressed to the first to fourth terminal apparatuses 101 to 104, respectively, which have been subjected to error correction coding. To modulation symbols for each subcarrier addressed to the fourth terminal apparatuses 101 to 104 are output.

  Multi-user MIMO signal generation section 203 receives each modulation symbol addressed to first to fourth terminal apparatuses 101-104, and inputs each modulation based on the CSI of each terminal apparatus acquired by CSI acquisition section 210. Signal processing is performed on the symbols, and multi-user MIMO symbols are generated for each of the antennas 208a to 208d of the antenna unit 208 used for transmission. Details of the multi-user MIMO signal generation unit 203 will be described later.

  First to fourth pilot multiplexing sections 204a, 204b, 204c and 204d multiplex pilot signals transmitted from antennas 208a to 208d of antenna section 208 into multiuser MIMO symbols transmitted from antennas 208a to 208d, respectively. To do. The pilot signals are preferably multiplexed so that the pilot signals transmitted from the respective antennas of the base station apparatus can be received in the terminal apparatuses 101 to 104 in a form that can be identified. Alternatively, it may be multiplexed by frequency division such as division by subcarriers, or may be multiplexed by code division.

  The first to fourth IFFT units 205a, 205b, 205c and 205d each perform multi-user MIMO signals for each antenna on which pilot signals are multiplexed, such as Inverse Fast Fourier Transform (IFFT). Frequency-time conversion is performed to convert the signal into a time domain signal.

  The first to fourth GI insertion units 206a, 206b, 206c, and 206d each insert a guard period (GI) into the time domain signal for each antenna.

  The first to fourth wireless transmission units 207 a, 207 b, 207 c, and 207 d transmit the signal with the GI inserted through the respective antennas 208 a to 208 d of the antenna unit 208.

  The control unit 211 controls each of the above units and causes each process to be executed.

  FIG. 3 is a functional block diagram illustrating a configuration example of the multiuser MIMO signal generation unit 203a when linear precoding is used. The multiuser MIMO signal generation unit 203 a includes a filter calculation unit 301 and a linear filter unit 302. In the example of FIG. 3, a multi-user MIMO signal is generated by linear precoding, particularly Zero-Forcing precoding.

The filter calculation unit 301 uses a CSI of each terminal device acquired by the CSI acquisition unit 210 shown in FIG. 2 as a channel having a complex channel gain between each antenna of the base station device 100 and the antenna of each terminal device as an element. A matrix H is generated for each subcarrier, and its inverse matrix H ⁻¹ (or pseudo inverse matrix H ^† = H ^H (HH ^H ) ⁻¹ ) is calculated as a weighting matrix W that is a linear filter.

  The linear filter unit 302 receives the modulation symbols addressed to the first to fourth terminal apparatuses 101 to 104 as inputs, multiplies the linear filter W calculated by the filter calculation unit 301 for each subcarrier, Multi-user MIMO symbols to be transmitted are output from antennas 208a to 208d, respectively.

  Thereby, when each terminal apparatus receives the multiuser MIMO symbol, interference (MUI) due to a signal other than the own terminal apparatus is canceled by linear precoding, and only the signal addressed to the own terminal apparatus is received.

In the multi-user MIMO signal generation unit 203a, the filter calculation unit 301 calculates and uses an inverse matrix as a linear filter. However, the present invention is not limited to this, and the weight matrix W = H ^H (HH ^H + αI) ⁻¹ (I represents a unit matrix and α represents a normalization coefficient) may be used as a linear filter. In this case, the MUI is not completely canceled during reception, but the signal-to-interference and noise power ratio (SINR) can be maximized, so that reception characteristics are improved.

  FIG. 4 is a functional block diagram illustrating a configuration example of the multiuser MIMO signal generation unit 203b when nonlinear precoding is used. In the example of FIG. 4, a multi-user MIMO signal is generated by nonlinear precoding, particularly Tomlinson-Harashima precoding (THP).

QR decomposition section (interference matrix calculation section) 404 uses complex propagation paths between each antenna of base station apparatus 100 and each terminal apparatus from the CSI of each terminal apparatus acquired by CSI acquisition section 210 shown in FIG. A channel matrix H having a gain as an element is generated for each subcarrier, QR decomposition is performed on Hermitian conjugate H ^H of the channel matrix ^H to decompose it into a unitary matrix Q and an upper triangular matrix R, and an upper triangular matrix R Hermite conjugate R ^H (which becomes a lower triangular matrix) is obtained, and an interference matrix B = (diagR ^H ) ⁻¹ R ^H −I representing the gain of the MUI between the terminal devices is obtained and output to the interference component calculation unit 403b. The unitary matrix Q is output to the linear filter unit 405. Note that diagX is a matrix having only the diagonal component of the matrix X, and I represents a unit matrix.

  The first remainder calculation unit 402a performs a remainder calculation on the modulation symbol addressed to the first terminal apparatus 101 generated by the first modulation unit 202a. In addition, since there is no MUI for the modulation symbol addressed to the first terminal apparatus 101, the interference component subtraction unit is omitted. Furthermore, the remainder calculation unit 402a can be omitted.

  Based on the interference matrix B obtained by the QR decomposition unit 404, the interference component calculation unit 403b generates a subtraction result of the modulation symbol of each subcarrier addressed to the first terminal apparatus 101 for each subaddress addressed to the second terminal apparatus 102. The interference component given to the modulation symbol of the carrier is calculated. Here, the element in the second row and the first column of the interference matrix B represents the complex gain of interference exerted by the modulation symbol addressed to the first terminal apparatus 101 on the modulation symbol addressed to the second terminal apparatus 102. The interference component can be calculated by multiplying the remainder calculation result of the modulation symbol addressed to the first terminal apparatus 101.

  The first interference component subtraction unit 401b uses the modulation symbol for the second terminal apparatus 102 calculated by the interference component calculation unit 403b from the modulation symbol for the second terminal apparatus 102 generated by the second modulation unit 202b. Is subtracted for each subcarrier.

  The second remainder calculation unit 402b performs a remainder calculation on the modulation symbol addressed to the second terminal apparatus 102 from which the interference component has been subtracted, using a modulo width predetermined by the modulation scheme.

  The interference component calculation unit 403b determines that the remainder calculation result of the modulation symbol of each subcarrier addressed to the first terminal apparatus 101 and the remainder calculation result of the modulation symbol of each subcarrier addressed to the second terminal apparatus 102 are the third terminal. The interference component given to the modulation symbol of each subcarrier addressed to apparatus 103 is calculated. Here, the element in the 3rd row and the 1st column of the interference matrix B represents the complex gain of interference exerted by the modulation symbol addressed to the first terminal apparatus 101 on the modulation symbol addressed to the third terminal apparatus 103, and 3 of the interference matrix B The elements in the second column represent the complex gains of interference that the modulation symbols addressed to the second terminal apparatus 102 have on the modulation symbols addressed to the third terminal apparatus 103, and each of these elements represents the first terminal apparatus 101. The interference component can be calculated by multiplying the remainder calculation result of the modulation symbol addressed to the remainder calculation result of the modulation symbol addressed to the second terminal apparatus 102.

  The second interference component subtraction unit 401c uses the modulation symbol for the third terminal apparatus 103 calculated by the interference component calculation unit 403b from the modulation symbol for the third terminal apparatus 103 generated by the third modulation unit 202c. Is subtracted for each subcarrier.

  The third remainder calculation unit 402c performs a remainder calculation on the modulation symbol addressed to the third terminal apparatus 103 from which the interference component has been subtracted, using a modulo width predetermined by the modulation scheme.

  The interference component calculation unit 403b is configured to generate a remainder calculation result of the modulation symbol of each subcarrier addressed to the first terminal apparatus 101, a remainder calculation result of the modulation symbol of each subcarrier addressed to the second terminal apparatus 102, and the third terminal. The remainder calculation result of the modulation symbol of each subcarrier addressed to apparatus 103 calculates an interference component given to the modulation symbol of each subcarrier addressed to fourth terminal apparatus 104. Here, the element in the 4th row and the 1st column of the interference matrix B represents the complex gain of interference that the modulation symbol addressed to the first terminal apparatus 101 has on the modulation symbol addressed to the fourth terminal apparatus 104, and 4 of the interference matrix B The element in the second row represents the complex gain of interference that the modulation symbol addressed to the second terminal apparatus 102 has on the modulation symbol addressed to the fourth terminal apparatus 104, and the element in the fourth row and third column of the interference matrix B represents the first element. 3 represents the complex gain of interference exerted on the modulation symbol addressed to the fourth terminal apparatus 104 by the modulation symbol addressed to the third terminal apparatus 103, and the remainder calculation result of the modulation symbol addressed to the first terminal apparatus 101 is included in these elements, respectively. The interference component can be calculated by multiplying the remainder calculation result of the modulation symbol addressed to the third terminal apparatus 103.

  The third interference component subtraction unit 401d modulates the modulation symbol addressed to the fourth terminal apparatus 104 calculated by the interference component calculation unit 403b from the modulation symbol addressed to the fourth terminal apparatus 104 generated by the fourth modulation unit 202d. Is subtracted for each subcarrier.

  The fourth remainder calculation unit 402d performs a remainder calculation on the modulation symbol addressed to the fourth terminal apparatus 104 from which the interference component has been subtracted, using a modulo width predetermined by the modulation scheme.

  The linear filter unit 405 generates a remainder calculation result of the modulation symbol addressed to the first terminal device 101 output from the first residue calculation unit 402a and the modulation addressed to the second terminal device 102 output from the second residue calculation unit 402b. The symbol residue calculation result, the modulation symbol residue calculation result for the third terminal device 103 output by the third residue calculation unit 402c, and the fourth terminal device 104 output by the fourth residue calculation unit 402d As a result, the unitary matrix Q calculated by the QR decomposition unit 404 is multiplied for each subcarrier as a linear filter, and multi-user MIMO symbols to be transmitted from the respective antennas of the antenna unit 208 are output. .

  Thereby, when each terminal apparatus receives the multi-user MIMO symbol, interference (MUI) due to a signal to other than the own terminal apparatus is canceled by THP, and only the signal addressed to the own terminal apparatus is received.

  In this embodiment, a method using QR decomposition of a channel matrix has been described as an example of a method for realizing THP. However, the present invention is not limited to this, and a method of V-BLAST (Vertical Bell Laboratories Layered Space Time) is used. A method described in Non-Patent Document 4 or the like that performs sub-optimization of rearrangement of terminal devices in THP may be used.

  FIG. 5 is a functional block diagram illustrating a configuration example of the multiuser MIMO signal generation unit 203c when linear precoding and nonlinear precoding are used in combination. In FIG. 5, linear precoding that uses THP as non-linear precoding and performs no remainder operation on the first terminal apparatus 101 and the second terminal apparatus 102, and the third terminal apparatus 103 and the fourth terminal An example in which the device 104 is combined with THP that performs remainder calculation is shown.

QR decomposition section (interference matrix calculation section) 404, as in the case of FIG. 4, determines between each antenna of base station apparatus 100 and the antenna of each terminal apparatus from the CSI of each terminal apparatus acquired by CSI acquisition section 210. Is generated for each subcarrier, QR decomposition is performed on Hermitian conjugate H ^H of the channel matrix ^H to decompose it into a unitary matrix Q and an upper triangular matrix R, and An Hermite conjugate R ^H (which becomes a lower triangular matrix) of the upper triangular matrix R is obtained, and an interference matrix B = (diagR ^H ) ⁻¹ R ^H −I representing the gain of the MUI between the terminal devices is obtained to obtain an interference component calculation unit. The unitary matrix Q is output to the linear filter unit 405.

  Based on the interference matrix B obtained by the QR decomposition unit 404, the interference component calculation unit 403c converts the modulation symbol of each subcarrier addressed to the first terminal apparatus 101 into the modulation symbol of each subcarrier addressed to the second terminal apparatus 102. The interference component given to is calculated. Here, the element in the second row and the first column of the interference matrix B represents the complex gain of interference exerted by the modulation symbol addressed to the first terminal apparatus 101 on the modulation symbol addressed to the second terminal apparatus 102. The interference component can be calculated by multiplying the modulation symbol addressed to the first terminal apparatus 101.

  The first interference component subtraction unit 401b uses the modulation symbol for the second terminal apparatus 102 calculated by the interference component calculation unit 403c from the modulation symbol for the second terminal apparatus 102 generated by the second modulation unit 202b. Is subtracted for each subcarrier.

  The interference component calculation unit 403c is configured so that the modulation symbol of each subcarrier addressed to the first terminal apparatus 101 and the modulation symbol of each subcarrier addressed to the second terminal apparatus 102 correspond to each subcarrier addressed to the third terminal apparatus 103. The interference component given to the modulation symbol is calculated. Here, the element in the 3rd row and the 1st column of the interference matrix B represents the complex gain of interference exerted by the modulation symbol addressed to the first terminal apparatus 101 on the modulation symbol addressed to the third terminal apparatus 103, and 3 of the interference matrix B The elements in the second column represent the complex gains of interference that the modulation symbols addressed to the second terminal apparatus 102 have on the modulation symbols addressed to the third terminal apparatus 103, and each of these elements represents the first terminal apparatus 101. The interference component can be calculated by multiplying the modulation symbol addressed to the modulation symbol addressed to the second terminal apparatus 102.

  The second interference component subtraction unit 401c uses the modulation symbol addressed to the third terminal device 103 generated by the third modulation unit 202c and the modulation symbol addressed to the third terminal device 103 calculated by the interference component calculation unit 403c. Is subtracted for each subcarrier.

  The third remainder calculation unit 402c performs a remainder calculation on the modulation symbol addressed to the third terminal apparatus 103 from which the interference component has been subtracted, using a modulo width predetermined by the modulation scheme.

  The interference component calculation unit 403c includes a modulation symbol for each subcarrier addressed to the first terminal apparatus 101, a modulation symbol for each subcarrier addressed to the second terminal apparatus 102, and each subcarrier addressed to the third terminal apparatus 103. An interference component given to the modulation symbol of each subcarrier addressed to the fourth terminal apparatus 104 by the remainder calculation result of the modulation symbol is calculated. Here, the element in the 4th row and the 1st column of the interference matrix B represents the complex gain of interference that the modulation symbol addressed to the first terminal apparatus 101 has on the modulation symbol addressed to the fourth terminal apparatus 104, and 4 of the interference matrix B The element in the second row represents the complex gain of interference that the modulation symbol addressed to the second terminal apparatus 102 has on the modulation symbol addressed to the fourth terminal apparatus 104, and the element in the fourth row and third column of the interference matrix B represents the first element. 3 represents the complex gain of interference exerted on the modulation symbol addressed to the fourth terminal apparatus 104 by the modulation symbol addressed to the third terminal apparatus 103. These elements include the modulation symbol addressed to the first terminal apparatus 101, the second The interference component can be calculated by multiplying the remainder calculation result of the modulation symbol addressed to the terminal apparatus 102 and the modulation symbol addressed to the third terminal apparatus 103.

  The third interference component subtraction unit 401d modulates the modulation symbol addressed to the fourth terminal apparatus 104 calculated by the interference component calculation unit 403c from the modulation symbol addressed to the fourth terminal apparatus 104 generated by the fourth modulation unit 202d. Is subtracted for each subcarrier.

  The fourth remainder calculation unit 402d performs a remainder calculation on the modulation symbol addressed to the fourth terminal apparatus 104 from which the interference component has been subtracted, using a modulo width predetermined by the modulation scheme.

  The linear filter unit 405 subtracts the modulation symbol generated by the first modulation unit 202a and addressed to the first terminal device 101 and the interference component output by the first interference component subtraction unit 401b. The modulation symbol addressed to, the remainder calculation result of the modulation symbol addressed to the third terminal device 103 output by the third residue calculation unit 402c, and the address of the fourth terminal device 104 output by the fourth residue calculation unit 402d The modulation symbol remainder calculation result is input, the unitary matrix Q calculated by the QR decomposition unit 404 is multiplied for each subcarrier as a linear filter, and multi-user MIMO symbols to be transmitted from each antenna of the antenna unit 208 are output.

  Thereby, when each terminal apparatus receives the multiuser MIMO symbol, interference (MUI) due to signals other than the terminal apparatus itself is caused by linear precoding for the first terminal apparatus 101 and the second terminal apparatus 102. The third terminal apparatus 103 and the fourth terminal apparatus 104 are canceled by the THP and only a signal addressed to the own terminal apparatus is received.

  FIG. 6A is a functional block diagram showing a configuration example of the terminal device 600 in the present embodiment.

  The radio reception unit 601 receives a signal from the base station apparatus 100 through the antenna unit 615.

  The GI removal unit 602 removes a guard interval (GI) from the received signal.

  The FFT unit 603 performs time-frequency conversion on the received signal from which the GI has been removed by Fast Fourier Transform (FFT) or the like, and converts it into modulation symbols for each subcarrier.

  Pilot separation section 604 separates the modulation symbols into received data symbols and pilot signal symbols, and inputs the received data symbols to propagation path compensation section 605 and pilot signal symbols to propagation path estimation section 609. .

  Propagation path estimation section 609, based on the separated symbols of the pilot signal, the propagation path state (complex propagation path gain) between each antenna of base station apparatus 100 and antenna 615 of terminal apparatus 600, and reception quality For example, estimate the received signal-to-noise power ratio (received SNR) or noise power.

  The propagation path compensation unit 605 performs propagation path compensation (equalization) on the received data symbols based on the propagation path state estimation result in the propagation path estimation unit 609.

  Based on the estimation result of the reception quality (reception SNR or noise power) in the propagation path estimation unit 609, the signal distribution estimation unit 610 assumes that the base station apparatus has not performed a remainder calculation (linear precoding). The received signal point distribution is calculated, and the signal point distribution estimation result is output.

  The signal distribution measurement unit 611 measures the signal point distribution of the received data symbol subjected to propagation path compensation, and outputs the signal point distribution measurement result.

  The remainder calculation determination unit 612 compares the signal point distribution estimation result and the signal point distribution measurement result, determines whether or not to perform the residue calculation, and outputs the determination result. Detailed processing in the signal distribution estimation unit 610, the signal distribution measurement unit 611, and the remainder calculation determination unit 612 will be described later.

  When a received data symbol that has been subjected to propagation path compensation is input to the remainder calculation unit 606 and a determination result that the remainder operation is performed is input from the remainder operation determination unit 612, a modulation scheme is applied to the received data symbol that has been subjected to propagation path compensation. When the determination result that the remainder operation is performed using the predetermined remainder operation width (modulo width) and the remainder operation is not performed is input, the propagation-compensated received data symbol is output as it is.

  Demodulation section 607 demodulates each received data symbol output from remainder calculation section 606.

  Decoding section 608 performs error correction decoding processing on the demodulated sequence to generate and output a received data sequence.

  The CSI generation unit 613 generates CSI that is channel state information based on the estimated propagation path state.

  The radio transmission unit 614 transmits the CSI generated by the CSI generation unit 613 to the base station apparatus 100 through the antenna unit 615.

  The control unit 616 controls each of the above units and executes each process.

  Next, a process for determining whether or not to perform a residue calculation in the signal distribution estimation unit 610, the signal distribution measurement unit 611, and the residue calculation determination unit 612 will be described. In the following description, the case of quadrature phase shift keying (QPSK) will be described as an example.

  FIG. 7 is a diagram showing a QPSK signal point arrangement diagram with the I axis of the in-phase component on the horizontal axis and the Q axis of the quadrature component on the vertical axis.

FIG. 7 shows an example in which the amplitudes of the I axis and the Q axis are determined so that the signal power becomes 1, and the four signal points of QPSK are (I, Q) = (1/2 ^1/2 , 1/2 ^{1/2), (-} 1/2 ^{1/2, 1/2} 1/2), (- ^{1/2 1/2} -1 / 2 1/2), ^{(1/2 1/2} located -1 ^{/ 2 1/2).}

Also, the modulo width τ of the remainder calculation in THP at this time is τ = 2 × 2 ^1/2 .

  Here, assuming that there is no noise at the time of reception by the terminal device (reception SNR = ∞), assuming that the propagation path compensation is perfect, and normalizing the received signal power to 1, the base station device performs the remainder calculation. The reception signal point arrangement when not applied (linear precoding) is the same as in FIG.

  Further, in the above assumption, when the base station apparatus performs a remainder calculation (THP), the received signal point arrangement is a form in which the QPSK signal point arrangement is repeated with a modulo width as shown in FIG. . At this time, the probability of distribution at the four points at the center portion divided by the modulo width and the signal points outside the center point is determined by the size of the MUI in multiuser MIMO.

FIG. 9 shows the probability density distribution of the signal amplitude for the received signal point at SNR = ∞ when the remainder calculation is not performed in the base station apparatus (linear precoding), focusing on the I axis (or Q axis). It is a graph. At this time, the probability density function f (x) of the signal amplitude is

It becomes. Here, δ (x) is a Dirac delta function.

However, noise is actually added to the received signal. Here, assuming that the added noise is Gaussian noise, the normal distribution of noise (Gaussian distribution) is superimposed on the two signal point distributions in FIG. If noise power (variance) and sigma _n ^2, the noise variance sigma _{n ^2/2} next to the I-axis (or the Q-axis), the signal amplitude of the probability density function f (x) is as shown in (2) Become.

At this time, the cumulative distribution function F (x) of the signal amplitude is as shown in the equation (3).

  Here, erf (x) is an error function.

If the propagation path estimation unit 609 estimates that SNR = γ (true value), the received signal power (excluding noise) is normalized to 1 by the propagation path compensation unit 605. Is obtained by σ _n ² = 1 / γ.

  In the signal distribution estimation unit 610, based on the reception quality (reception SNR or noise power) estimated by the propagation path estimation unit 609, the residue calculation is not performed in the base station apparatus using the equation (2) (linear precoding). The signal amplitude distribution of the received signal in the case of coding) is estimated. Hereinafter, this estimation result is referred to as an estimated distribution.

  FIG. 10 is a graph showing a result of estimating the probability density distribution of the signal amplitude of the received signal when the received signal power is normalized to 1 at SNR = 3 dB using the equation (2).

  The one-dot chain line in FIG. 10 indicates the modulo width of the remainder calculation, and the portion exceeding the modulo width in the probability density distribution is indicated by diagonal lines.

  The signal distribution measurement unit 611 measures the signal amplitude distribution using a plurality of received data symbols that have undergone propagation path compensation. Hereinafter, this measurement result is referred to as a measurement distribution.

  FIG. 11 is an example of a measurement distribution obtained by computer simulation of the signal amplitude distribution (frequency distribution, histogram) at the reception SNR = 3 dB when the base station apparatus is not subjected to residue calculation (linear precoding). is there. The one-dot chain line in FIG. 11 indicates the modulo width of the remainder calculation as in FIG.

  Furthermore, FIG. 12 is an example of a measurement distribution obtained by computer simulation of the signal amplitude distribution (frequency distribution, histogram) at the reception SNR = 3 dB when the residue calculation is performed in the base station apparatus (THP). . The alternate long and short dash line in FIG. 12 also indicates the modulo width of the remainder calculation.

  6A compares the estimated distribution in the signal distribution estimation unit 610 with the measurement distribution in the signal distribution measurement unit 611, and determines whether or not the remainder calculation unit 606 performs the residue calculation.

  As an example, the estimated distribution of FIG. 10 and the shape of the measurement distribution of FIG. 11 or FIG. 12 are compared. If the degree of coincidence between the two is high, the remainder calculation is not performed, and the degree of coincidence is low (the measurement distribution is flatter and the distribution is lower). If the range is wide), it is determined that the remainder calculation is performed.

  In this example, FIG. 11 is closer to FIG. 11 than FIG.

  As an evaluation of the degree of coincidence, for example, the shape of the measurement distribution is approximated by a polynomial, the correlation coefficient between the approximation result and the estimated distribution is calculated, and when the correlation is high (close to a preset threshold value close to 1) When the degree is high and the correlation is low (less than a preset threshold value), the degree of coincidence is low, or when the integration result of the absolute value of the difference between the estimated distribution and the measured distribution is small (close to a preset threshold value close to 0) Less than), the degree of coincidence is high. The preset threshold value, for example, maximizes the probability of correctly determining whether or not to perform a residue operation (whether or not the residue operation has been performed) and minimizes the probability of erroneous determination. Thus, a method of determining by computer simulation or the like is preferable.

As another example, the ratios of the estimated distribution and the measured distribution that are distributed outside the modulo width (outside the one-dot chain line in FIGS. 10, 11, and 12) are obtained and compared. If so, the remainder calculation is not performed, and if the measurement distribution is larger, it is determined that the remainder calculation is performed. Here, the ratio (probability) p distributed outside the modulo width of the estimated distribution in the above example is expressed by Equation (4) using the cumulative distribution function F (x) of Equation (3).

  The ratio distributed outside the modulo width of the measurement distribution can be obtained from the total number of received data symbols and the ratio of the number distributed outside the modulo width. Note that the determination of whether the above-mentioned ratio is about the same or the measurement distribution is larger is, for example, the probability of correctly determining whether or not to perform a residue calculation (whether or not a residue calculation has been performed on the transmission side). It is preferable to determine the threshold value by computer simulation or the like so as to minimize the probability of maximizing and erroneous determination, and determining by comparing the difference between the two ratios with the threshold value. If the error is not included in the propagation path estimation result, the above ratio will not be smaller in the measurement distribution, but if the measurement distribution is smaller (more than the same level), the remainder calculation is performed. It is preferable to perform a process such as determining not to perform or re-executing a more accurate propagation path estimation.

  When linear precoding (no residue calculation) and THP (with residue calculation) are selected and used for each subcarrier, the signal distribution estimation and measurement are performed for each subcarrier.

  Although the case of QPSK has been described above, in the case of other modulation schemes as well, it is possible to determine whether or not to perform a remainder operation by comparing the estimated distribution with the measured distribution.

  Also, in this embodiment, when it is determined that the terminal device on the reception side performs the residue calculation in the residue calculation determination unit 612 (the residue calculation is performed in the base station device), the demodulation unit 607 performs demodulation ( The example in which the residue calculation is performed on the reception data symbol that has been subjected to propagation path compensation in the residue calculation unit 606 before the reception signal point determination) has been described.

  FIG. 6B shows a configuration example of a terminal device according to another embodiment of the present invention. Unlike the terminal device 600 in FIG. 6A, the terminal device 600b in FIG. 6B does not include the remainder calculation unit 606. If the demodulation unit 607b determines that the residue calculation determination unit 612 performs the residue calculation, the received signal point arrangement (candidate signal point arrangement) in the absence of noise has a modulo width as shown in FIG. In consideration of the fact that the signal point arrangement at the time of modulation in the station apparatus is repeated, demodulation is performed from the Euclidean distance between the received signal point (with noise added) and each candidate signal point repeated with a modulo width. A log Likelihood Ratio (LLR) of bits is calculated (demodulation processing by soft decision).

  The LLR is input to the decoding unit 608 to perform error correction decoding. Here, the calculation of the LLR in the demodulator 607b can be performed by, for example, a known method described in Equation (15) to Equation (20) of Non-Patent Document 6. That is, it can be calculated using an algorithm that calculates the LLR using the Euclidean distance between the received signal point and the candidate signal point close to the received signal point among the candidate signal points repeated with a modulo width.

  The configuration shown in FIG. 6B can be similarly applied to the terminal devices of the following embodiments.

  According to the present embodiment, when a base station apparatus that performs multi-user MIMO using linear precoding and a base station apparatus that performs multi-user MIMO using THP are mixed, or when the base station apparatus uses multi-user MIMO and THP based on linear precoding. When the base station apparatus performs both of multi-user MIMO and the base station apparatus performs multi-user MIMO by combining linear precoding and THP at the same time, the terminal apparatus notifies the base station apparatus by control information or the like. Without determining whether the multi-user MIMO signal for the terminal device is linear precoding (no residue calculation is performed) or THP (residue calculation is performed) based on the distribution of the received signal Whether or not there is a remainder operation in the reception process. Sincerely it is possible to detect the reception data by switching.

  In particular, when the base station apparatus supports both interference suppression by linear precoding and interference suppression by THP, or as in Non-Patent Document 5, the base station apparatus performs interference suppression by simultaneously combining linear precoding and THP. In some cases, depending on the instantaneous propagation path state between the base station device and the terminal device, the state of interference, and the combination of terminal devices that perform spatial multiplexing in multiuser MIMO, the terminal device (user) ), And further in OFDM, there is a possibility that switching between interference suppression by linear precoding and interference suppression by THP may be performed for each subcarrier, and even if the switching information is notified by 1 bit, the amount of control information is 1 transmission. Every time (number of receiving devices) × (number of subcarriers) bits are required, but according to the present embodiment, the control information is The cornerstone.

(Second Embodiment)
Next, a communication technique according to the second embodiment of the present invention will be described. Also in the present embodiment, the base station apparatus performs multiuser MIMO transmission from the first terminal apparatus to the four terminal apparatuses of the fourth terminal apparatus, and linearizes the MUI generated between the streams destined for each terminal apparatus. A communication system that performs transmission by suppressing in advance by precoding or nonlinear precoding (THP) will be described as an example. In addition, the structure of the base station apparatus in this Embodiment is the same as 1st Embodiment (FIG. 2).

  FIG. 13 is a functional block diagram showing a configuration example of the terminal device 1300 in the present embodiment.

  The terminal device 1300 in FIG. 13 is partially different in configuration and operation from the terminal device 600 in FIG. 6A (or FIG. 6B). Hereinafter, in the terminal device 1300, a description will be given of portions that are different from the operation of the terminal device 600 in FIG.

  Based on the estimation result of the reception quality (reception SNR or noise power) in the propagation path estimation unit 609, the signal variance estimation unit 1310 is based on the assumption that no residue calculation is performed in the base station apparatus (linear precoding). The variance of the distribution of received signal points is calculated, and the signal point variance estimation result is output.

  The signal dispersion measurement unit 1311 measures the dispersion of the signal point distribution of the received data symbol subjected to propagation path compensation, and outputs a signal point dispersion measurement result.

  The residue calculation determination unit 1312 compares the signal point variance estimation result with the signal point variance measurement result, determines whether or not to perform residue calculation, and outputs the determination result.

  Next, processing for determining whether or not to perform remainder calculation in the signal variance estimation unit 1310, the signal variance measurement unit 1311, and the remainder calculation determination unit 1312 will be described. In the following description, QPSK will be described as an example, as in the first embodiment.

  Based on the reception quality (reception SNR or noise power) estimated by the propagation path estimation unit 609, the signal variance estimation unit 1310 receives a signal of a reception signal when no residue calculation is performed in the base station apparatus (linear precoding) Estimate the variance of the amplitude distribution.

At this time, assuming that there is no noise at the time of reception by the terminal device (reception SNR = ∞), it is assumed that the propagation path compensation is perfect, and the received signal power (that is, received signal variance σ _s ² ) is normalized to 1. Then, the distribution of the signal amplitude of the received signal point on the I axis (or Q axis) is as shown in FIG. 9, and the variance of the received signal on the I axis (or Q axis) is σ _s ² /2=0.5. Become.

Further, when the variance of the noise (the noise power) and sigma _n ^2, the variance of the noise of the I-axis (or the Q axis) is σ _n ^2/2.

Since the occurrence probability of signal points and the occurrence probability of noise are independent, the variance σ _rxe ² of the distribution of the received signal actually added with noise can be estimated from the equation (5).

  Hereinafter, this estimation result is referred to as estimated variance.

The signal dispersion measuring unit 1311 measures the dispersion σ _rxs ² of the signal amplitude using a plurality of received data symbols subjected to propagation path compensation. Specifically the amplitude _x i of the I-axis of N received data symbols (or Q axis) (i = 1 to N), obtained by (6).

Here, x _avg is an average value of x _i (i = 1 to N). Hereinafter, this measurement result is referred to as measurement dispersion.

  The remainder calculation determination unit 1312 compares the estimated variance in the signal variance estimation unit 1310 with the measurement variance in the signal variance measurement unit 1311 and determines whether or not the remainder calculation unit 606 performs the residue calculation. Specifically, when the estimated variance is equal to the measured variance (within a certain error range), the remainder calculation is not performed, and when the measured variance is larger than the estimated variance (greater than a predetermined ratio), the remainder calculation is performed. Is determined.

  In other words, when it is determined that the estimated variance and the measured variance are equal, it is necessary to consider an error. If it is determined that they are equal within a certain error range, the remainder operation is not performed. When the error is larger than the error, a remainder calculation is performed.

  The determination of whether the above variance is equal or the measurement variance is larger is, for example, maximizing the probability that it is possible to correctly determine whether or not to perform a residue operation (whether or not the residue operation has been performed). A method of determining a threshold value by computer simulation or the like so as to minimize the probability of determination and determining by comparing a difference between two variances with the threshold value is preferable. If there is no error in the propagation path estimation result, the measurement variance will not be smaller, but if the measurement variance is smaller (more than the same level), the remainder calculation is not performed. It is preferable to perform processing such as determination or re-execution of more accurate propagation path estimation.

  When linear precoding (no residue calculation) and THP (with residue calculation) are selected and used for each subcarrier, the estimation and measurement of the variance of the signal distribution is performed for each subcarrier.

  In the above description, the case of QPSK has been described. Similarly, in the case of other modulation schemes, it is possible to determine whether or not to perform a remainder calculation by comparing the estimated variance and the measured variance.

  As described above, according to the present embodiment, a base station apparatus that performs multi-user MIMO using linear precoding and a base station apparatus that performs multi-user MIMO using THP are mixed, or the base station apparatus uses linear precoding. In the case of supporting both multiuser MIMO by coding and multiuser MIMO by THP, and when the base station apparatus performs multiuser MIMO by simultaneously combining linear precoding and THP, the terminal apparatus Whether the multi-user MIMO signal for the terminal device is linear precoding (no residue calculation is performed) or THP (residue calculation is performed) without receiving notification by control information from It is possible to make a decision based on the distribution of the signal distribution and receive It is possible to detect the reception data properly or deactivates modulo operation in sense.

  In particular, when the base station apparatus supports both interference suppression by linear precoding and interference suppression by THP, or as in Non-Patent Document 5, the base station apparatus performs interference suppression by simultaneously combining linear precoding and THP. In some cases, depending on the instantaneous propagation path state between the base station device and the terminal device, the state of interference, and the combination of terminal devices that perform spatial multiplexing in multiuser MIMO, the terminal device (user) ), And further in OFDM, there is a possibility that switching between interference suppression by linear precoding and interference suppression by THP may be performed for each subcarrier, and even if the switching information is notified by 1 bit, the amount of control information is 1 transmission. Every time (number of receiving devices) × (number of subcarriers) bits are required, but according to the present embodiment, the control information is The cornerstone.

(Third embodiment)
In the present embodiment, the base station apparatus performs multi-user MIMO transmission from the first terminal apparatus to the four terminal apparatuses of the fourth terminal apparatus, and linearly pre-creates the MUI generated between streams destined for each terminal apparatus. A communication system in which transmission is suppressed in advance by coding or nonlinear precoding (THP) will be described as an example.

  The configuration of the base station apparatus in the present embodiment is the same as that in the first embodiment (FIG. 2). FIG. 14 is a block diagram illustrating a configuration example of the terminal device 1400 in the present embodiment.

  The terminal device 1400 in FIG. 14 is partially different in configuration and operation from the terminal device 600 in FIG. 6A (or FIG. 6B).

  Hereinafter, a description will be given of parts that are different in operation from the terminal device 600 of FIG.

  The remainder calculation determination unit 1412 selects one or a plurality of subcarriers (or frequency channels) with good reception quality (high channel gain or reception SNR) from the reception quality estimation result by the channel estimation unit 609, and A received data symbol subjected to propagation path compensation in the selected subcarrier is extracted, and the in-phase component (I axis) and / or quadrature component (Q axis) of the signal point of the received data symbol is outside the modulo width ( It is determined that the remainder calculation is performed when it is located outside the area surrounded by the broken line in the center in FIG. 8, and it is determined that the remainder calculation is not performed when neither the I-axis component nor the Q-axis component exceeds the modulo width. To do. When a plurality of received data symbols are selected in the above, it is determined that the remainder calculation is performed when any one of them exceeds the modulo width. Also, in the case of a single carrier transmission system instead of OFDM, the above determination is performed by selecting a (time) symbol having a good reception state from the propagation path estimation result.

  According to the present embodiment, when a base station apparatus that performs multi-user MIMO using linear precoding and a base station apparatus that performs multi-user MIMO using THP are mixed, or when the base station apparatus uses multi-user MIMO and THP based on linear precoding. When the base station apparatus performs both of multi-user MIMO and the base station apparatus performs multi-user MIMO by combining linear precoding and THP at the same time, the terminal apparatus notifies the base station apparatus by control information or the like. None, whether or not the multi-user MIMO signal for the terminal apparatus is linear precoding (no residue calculation is performed) or THP (residue calculation is performed). That is, the noise power is relatively small and It is possible to determine on the basis of the signal point position of low received data symbols probability exceeding modulo width, we are possible to detect the reception data properly or deactivates modulo operation in the receiving process.

  In particular, when the base station apparatus supports both interference suppression by linear precoding and interference suppression by THP, or as in Non-Patent Document 5, the base station apparatus performs interference suppression by simultaneously combining linear precoding and THP. In some cases, depending on the instantaneous propagation path state between the base station device and the terminal device, the state of interference, and the combination of terminal devices that perform spatial multiplexing in multiuser MIMO, the terminal device (user) ), There is a possibility of switching between interference suppression by linear precoding and interference suppression by THP, and even if the switching information is reported in 1 bit, the control information amount is (number of receiving devices) bits for each transmission. Although necessary, according to the present embodiment, control information is not necessary.

(Fourth embodiment)
In this embodiment, the base station apparatus performs multi-user MIMO transmission from the first terminal apparatus to the four terminal apparatuses of the fourth terminal apparatus, and inter-user interference ( A communication system in which MUI) is previously suppressed by linear precoding or non-linear precoding (THP) and transmitted will be described as an example.

  The configuration of the base station apparatus in the present embodiment is the same as that in FIG. 2, but the detailed configuration of multiuser MIMO signal generation section 203 is different.

  FIG. 15 is a block diagram illustrating a configuration example of a multiuser MIMO signal generation unit in the present embodiment when linear precoding and nonlinear precoding are used in combination. In FIG. 15, THP is used as nonlinear precoding, and linear precoding is performed in which no remainder operation is performed on the first terminal apparatus 101 and the second terminal apparatus 102, and the third terminal apparatus 103 and the fourth terminal. An example in which the device 104 is combined with THP that performs remainder calculation is shown.

  The multi-user MIMO signal generation unit 203d in FIG. 15 is partially different in configuration and operation from the multi-user MIMO signal generation unit 203c in FIG. Add additional vectors to it. This addition of the additional vector is performed so that when the remainder calculation is performed in the base station apparatus, the symbols are surely distributed outside the modulo width when received by the terminal apparatus.

  Hereinafter, a description will be given of parts that are different in operation from those of the multiuser MIMO signal generation unit 203c in FIG.

  The processing related to the modulation symbol addressed to the first terminal apparatus 101 and the modulation symbol addressed to the second terminal apparatus 102 is the same as that of the multiuser MIMO signal generation unit 203c in FIG.

  The third vector adder 1501c applies the I-axis or the partial symbol to the partial calculation result of the modulation symbol of each subcarrier addressed to the third terminal apparatus 103 output from the third remainder calculator 402c. An additional vector having a length that is an integral multiple of the modulo width is added to the Q-axis component or both components. In addition, although it is preferable that the position (subcarrier, OFDM symbol) of the part of the symbols to which the additional vector is added is determined in advance by the system, the present invention is not limited to this. Also, the interference vector calculation section 403d receives the third vector addition section 1501c instead of the remainder calculation result of the modulation symbol of each subcarrier addressed to the third terminal apparatus output from the third remainder calculation section 402c. The result of adding the additional vector is input.

  The interference component calculation unit 403d includes a modulation symbol for each subcarrier addressed to the first terminal apparatus 101, a modulation symbol for each subcarrier addressed to the second terminal apparatus 102, and each subcarrier addressed to the third terminal apparatus 103. The interference component given to the modulation symbol of each subcarrier addressed to the fourth terminal apparatus 104 by the symbol obtained by adding the additional vector to the modulation symbol remainder calculation result is calculated. Here, the element in the 4th row and the 1st column of the interference matrix B represents the complex gain of interference that the modulation symbol addressed to the first terminal apparatus 101 has on the modulation symbol addressed to the fourth terminal apparatus 104, and 4 of the interference matrix B The element in the second row represents the complex gain of interference that the modulation symbol addressed to the second terminal apparatus 102 has on the modulation symbol addressed to the fourth terminal apparatus 104, and the element in the fourth row and third column of the interference matrix B represents the first element. 3 represents the complex gain of interference exerted on the modulation symbol addressed to the fourth terminal apparatus 104 by the modulation symbol addressed to the third terminal apparatus 103. These elements include the modulation symbol addressed to the first terminal apparatus 101, the second An interference component can be calculated by multiplying the remainder calculation result of the modulation symbol addressed to the terminal apparatus 102 and the modulation symbol addressed to the third terminal apparatus 103 by the symbol obtained by adding the additional vector.

  The third interference component subtraction unit 401d modulates the modulation symbol addressed to the fourth terminal device 104 calculated by the interference component calculation unit 403d from the modulation symbol addressed to the fourth terminal device 104 generated by the fourth modulation unit 202d. Is subtracted for each subcarrier.

  The fourth remainder calculation unit 402d performs a remainder calculation on the modulation symbol addressed to the fourth terminal apparatus 104 from which the interference component has been subtracted, using a modulo width predetermined by the modulation scheme.

  The fourth vector adder 1501d applies the I-axis or the partial symbol to the partial calculation result of the modulation symbol of each subcarrier addressed to the fourth terminal apparatus 104 output from the fourth remainder calculator 402d. An additional vector having a length that is an integral multiple of the modulo width is added to the Q-axis component or both components. In addition, although it is preferable that the position (subcarrier, OFDM symbol) of the part of the symbols to which the additional vector is added is determined in advance by the system, the present invention is not limited to this.

  The linear filter unit 405 subtracts the modulation symbol generated by the first modulation unit 202a and addressed to the first terminal device 101 and the interference component output by the first interference component subtraction unit 401b. The modulation symbol addressed to, the symbol obtained by adding the additional vector to the remainder calculation result of the modulation symbol addressed to the third terminal apparatus 103 output from the third vector adding unit 1501c, and the fourth vector output from the fourth vector adding unit 1501d. 4, a symbol obtained by adding an additional vector to the remainder calculation result of the modulation symbol addressed to the terminal device 104 is input, and the unitary matrix Q calculated by the QR decomposition unit 404 is multiplied for each subcarrier as a linear filter. A multi-user MIMO symbol to be transmitted from each antenna is output.

  FIG. 16 shows a conceptual diagram of additional vector addition in the third vector addition unit 1501c and the fourth vector addition unit 1501d. Hereinafter, the case of QPSK will be described as an example.

  The modulation symbol addressed to the third terminal apparatus 103 or the modulation symbol addressed to the fourth terminal apparatus 104 output from the third modulation section 202c or the fourth modulation section 202d is a signal indicated by A in FIG. Suppose it was a point. If the result obtained by subtracting the interference component in the second interference component subtraction unit 401c or the third interference component subtraction unit 401d is point B, the residue in the third residue calculation unit 402c or the fourth residue calculation unit 402d. The result of the calculation is point C (the perturbation vector from point B to point C is added by the remainder calculation). Here, the result of the remainder calculation is distributed in a region painted with diagonal lines in FIG. 16 for all symbols. In the third vector adder 1501c and the fourth vector adder 1501d, the I-axis and / or Q-axis components of the partial symbols of the remainder calculation result each have a length that is an integral multiple of the modulo width. Add additional vectors. The example of FIG. 16 shows a case where an additional vector (−τ, 0) having a length of 1 times the modulo width τ is added to only the in-phase component, and is added to the remainder calculation result at the C point. The vector is added to output point D.

  FIG. 17 shows an example of received signal point arrangement (when there is no noise) in a terminal device whose MUI has been canceled by THP.

  Due to the remainder calculation at the time of transmission in the base station apparatus, at the time of reception at the terminal apparatus, as shown in FIG. 17, it is received in a form in which signal points are repeated for each modulo width. In FIG. 16, point D added with the additional vector is E point where the interference component is canceled and the perturbation vector and the additional vector obtained by the remainder calculation at the time of transmission are added to the signal point A of the original modulation symbol at the time of transmission. Received.

  The additional vector addition in the third vector addition unit 1501c and the fourth vector addition unit 1501d described above has a modulo width when the symbol is received by the terminal device when the remainder calculation is performed in the base station device. This is done so that it is distributed outside.

  Therefore, when the signal point is moved by the remainder calculation in the third remainder calculation unit 402c or the fourth remainder calculation unit 402d, that is, in the example of FIG. 16, the point B and the point C are different (the size of the perturbation vector is 0). In such a case, the received signal point at the terminal device is located outside the modulo width (in the absence of noise) even if the additional vector is not added. In such a case, it is not always necessary to add the additional vector. Absent. When adding an additional vector, if the perturbation vector added as a result of the remainder operation is v, an additional vector different from the opposite vector -v is added, so that the received signal point has a modulo width. It can be located outside.

  In addition, when the signal point is not moved by the remainder calculation in the third remainder calculation unit 402c or the fourth remainder calculation unit 402d, that is, in the example of FIG. 16, the point B and the point C are the same (the size of the perturbation vector is the same). 0), the received signal point at the terminal device is located inside the modulo width (when there is no noise), so that the received signal point at the terminal device is outside the modulo width by adding an additional vector. Can be positioned. In this case, the direction of the additional vector may be any direction.

  Note that, since the transmission power increases due to the addition of the additional vector, it is preferable that the size of the additional vector be the minimum necessary (such as a length of about 1 time the modulo width on the I-axis and / or the Q-axis). If the noise power is large and the received SNR is low, add a larger additional vector (such as a length more than twice the modulo width to the I-axis and / or the Q-axis) to facilitate internal / external modulo width determination. You may do it. In addition, the transmission power may be readjusted after adding the additional vector.

  The configuration of the terminal device in this embodiment may be any of the configuration of the terminal device 600 in FIG. 6A (or FIG. 6B), the terminal device 1300 in FIG. 13, or the terminal device 1400 in FIG. Here, taking the terminal device 1400 of FIG. 14 as an example, a remainder calculation determining unit 1412 having a detailed operation different from that of the third embodiment will be described.

  Residue calculation determining section 1412 in the present embodiment selects a received data symbol whose position (subcarrier, OFDM symbol) has been previously determined in the system, and the I-axis or Q of the signal point of the selected received data symbol If the axis or both components are located outside the modulo width, it is determined that the remainder calculation is performed, and if neither the I-axis component nor the Q-axis component exceeds the modulo width, the remainder calculation is not performed. judge. In addition, when there are multiple received data symbols whose positions are determined in advance by the system, considering that the received signal point fluctuates due to noise, out of the multiple received data symbols, If the received data symbols located outside the modulo width of the I-axis or Q-axis component or both of the components are a majority, it is determined that the remainder calculation is performed, and if it is less than the majority, it is determined that the remainder calculation is not performed. It is preferable to do this.

  Note that the additional vector added by the base station apparatus is automatically removed by the remainder calculation of the remainder calculation unit 606, so that it is not necessary to perform processing such as subtraction in the terminal apparatus.

  In this way, in the base station apparatus, in the case of THP for performing the remainder calculation, by adding the additional vector to the remainder calculation result of a part of the symbols, the symbol added with the additional vector is added in the terminal apparatus. The signal is received at the signal point position shifted by the vector and located outside the modulo width. For this reason, if the presence or absence of the remainder calculation is determined based on the symbol, the determination can be made with higher accuracy.

  In each of the above embodiments, a communication system that transmits and receives data while suppressing MUI in multiuser MIMO using linear precoding and THP has been described. However, the scope of the present invention is not limited to this. For example, a communication system that suppresses inter-symbol interference using linear precoding and THP, a communication system that suppresses inter-cell interference using linear precoding and THP, and the like. The present invention can be similarly applied to wired and wireless communication systems to be suppressed.

  The program that operates in the communication apparatus according to the present invention may be a program that controls a CPU (Central Processing Unit) or the like (a program that causes a computer to function) 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 RAM (Random Access Memory) during the processing, and then stored in various ROMs such as Flash ROM (Read Only Memory) and HDD (Hard Disk Drive). Reading, correction, and writing are performed by the CPU as necessary.

  6A and 6B are recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed. You may perform the process of each part. Here, the “computer system” includes an OS and hardware such as peripheral devices.

  The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory in a computer system serving as a server or a client in that case, and a program that holds a program for a certain period of time are also included. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system. Further, part or all of the communication devices (base station device and terminal device) in the above-described embodiment may be realized as an LSI that is typically an integrated circuit. Each functional block of the communication device may be individually chipped, or part or all of them may be integrated into a chip. Further, the method of circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. In addition, when an integrated circuit technology that replaces LSI appears due to progress in semiconductor technology, an integrated circuit based on the technology can also be used.

  The embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to these embodiments, and design changes and the like can be made without departing from the scope of the present invention. Inventions are also included.

  The present invention is applicable to a communication device.

DESCRIPTION OF SYMBOLS 100 ... Base station apparatus, 101-104 ... 1st-4th terminal device, 201 ... Encoding part, 202 ... Modulation part, 203 ... Multiuser MIMO signal generation part, 204 ... Pilot multiplexing part, 205 ... IFFT part 207 206 GI insertion unit 207 Radio transmission unit 208 Antenna unit 209 Radio reception unit 210 CSI acquisition unit 301 Filter calculation unit 302 Linear filter unit 401 Interference subtraction unit 402 Residue calculation unit, 403b ... interference component calculation unit, 404 ... QR decomposition unit, 600 ... terminal device, 601 ... radio reception unit, 602 ... GI removal unit, 603 ... FFT unit, 604 ... pilot separation unit, 605 ... propagation compensation 606: Remainder calculation unit, 607 ... Demodulation unit, 608 ... Decoding unit, 609 ... Propagation path estimation unit, 610 ... Signal distribution estimation unit, 613 ... CSI generation unit, 6 4 ... wireless transmission unit, 615 ... antenna unit, 616 ... control unit, 1310 ... signal variance estimation unit, 1311 ... signal variance measuring unit, 1312 ... remainder operation determination unit.

  All publications, patents and patent applications cited herein are incorporated herein by reference in their entirety.

Claims (13)

A reception device that receives a signal in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or used simultaneously,
A residue calculation determination unit that determines whether to perform a residue calculation on the received signal based on the reception quality estimated from the received signal and the distribution of the received signal measured from the received signal;
A receiving apparatus, comprising: a residue calculation unit that performs a residue calculation on a received signal when the determination result is a residue calculation. A reception device that receives a signal in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or used simultaneously,
A channel estimator for estimating the reception quality of the received signal;
Based on the estimation result of the reception quality, a signal distribution estimation unit that estimates the distribution of received signal points when it is assumed that no residue calculation is performed at the time of transmission;
A signal distribution measuring unit for measuring the signal point distribution of the received signal;
A remainder calculation determination unit that compares the estimation result of the reception signal point distribution with the measurement result of the reception signal point distribution and determines whether or not to perform a residue calculation on the reception signal;
When the determination result is a residue calculation, a residue calculation unit that performs a residue calculation on the received signal;
Receiving device, characterized in that it comprises a. The remainder calculation determination unit
  If the degree of coincidence between the estimation result of the reception signal point distribution and the distribution shape of the measurement result of the reception signal point distribution is high, it is determined that the remainder calculation is not performed,
  The receiving apparatus according to claim 2, wherein when the degree of coincidence is low, it is determined that a remainder calculation is performed. The remainder calculation determination unit
When the ratio of distribution outside the modulo width in the estimation result of the received signal point distribution is substantially equal to the ratio of distribution outside the modulo width in the measurement result of the reception signal point distribution, a remainder calculation is performed. It is determined that
The receiving apparatus according to claim 2 , wherein when the ratio in the measurement result of the received signal point distribution is larger, it is determined that the remainder calculation is performed . A reception device that receives a signal in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or used simultaneously,
  A channel estimator for estimating the reception quality of the received signal;
  Based on the estimation result of the reception quality, a signal variance estimation unit that estimates the variance of the distribution of received signal points when it is assumed that no residue calculation is performed at the time of transmission;
  A signal dispersion measurement unit for measuring the dispersion of the signal point distribution of the received signal;
  A remainder calculation determination unit that compares the estimation result of the variance of the received signal point distribution with the measurement result of the variance of the received signal point distribution and determines whether to perform a remainder calculation on the received signal;
  When the determination result is a residue calculation, a residue calculation unit that performs a residue calculation on the received signal;
A receiving apparatus comprising: The remainder calculation determination unit
  When the estimation result of the variance of the received signal point distribution and the measurement result of the variance of the received signal point distribution are substantially equal, it is determined that the remainder calculation is not performed,
  6. The receiving apparatus according to claim 5, wherein when the variance of the received signal point distribution measurement is larger, it is determined that the remainder calculation is performed. A reception device that receives a signal in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or used simultaneously,
  A channel estimator for estimating the reception quality of the received signal;
  If one or more subcarriers or frequency channels with good reception quality estimation results are selected and the signal point of the received data symbol in the selected subcarrier or frequency channel is located outside the modulo width, a remainder operation is performed. A remainder calculation determination unit that determines that the remainder calculation is not performed when it is located inside the modulo width;
  When the determination result is a residue calculation, a residue calculation unit that performs a residue calculation on the received signal;
A receiving apparatus comprising: A reception device that receives a signal in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or used simultaneously,
A residue calculation determination unit that determines whether to perform a residue calculation on the received signal based on the reception quality estimated from the received signal and the distribution of the received signal measured from the received signal;
A demodulator that performs likelihood calculation in consideration of repetition of signal points by a residue calculation from a received signal when the determination result is a residue calculation;
Receiving apparatus characterized by having a. A reception device that receives a signal in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or used simultaneously,
A channel estimator for estimating the reception quality of the received signal ;
If one or more subcarriers or frequency channels with good reception quality estimation results are selected and the signal point of the received data symbol in the selected subcarrier or frequency channel is located outside the modulo width, a remainder operation is performed. A remainder calculation determination unit that determines that the remainder calculation is not performed when it is located inside the modulo width ;
A demodulator that performs likelihood calculation in consideration of repetition of signal points by a residue calculation from a received signal when the determination result is a residue calculation ;
Receiving device, characterized in that it comprises a. A transmitter that transmits a signal by suppressing interference in a receiver in advance by nonlinear precoding,
  An interference component subtraction unit for subtracting the interference component from the modulation symbol;
  A residue calculation unit that performs a residue calculation on the modulation symbol from which the interference component has been subtracted;
  A vector adder that adds an additional vector having a component that is an integral multiple of the modulo width of the remainder operation to some symbols of the remainder operation result;
A transmission device comprising:   The transmitting apparatus according to claim 10, wherein positions of the partial symbols to which an additional vector is added are determined in advance. A reception device that receives a signal in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or used simultaneously,
A predetermined part of the received data symbols is selected, and if the signal point of the selected received data symbol is located outside the modulo width, it is determined that a remainder operation is performed, and the inside of the modulo width is determined. A remainder calculation determination unit that determines not to perform a residue calculation when located in
When the determination result is a residue calculation, a residue calculation unit that performs a residue calculation on the received signal;
A receiving apparatus comprising: A communication method in which interference suppression by linear precoding and interference suppression by nonlinear precoding are selectively used or used simultaneously,
  A channel estimation step for estimating the reception quality of the received signal;
  Based on the estimation result of the reception quality, a signal distribution estimation step for estimating the distribution of received signal points when it is assumed that no residue calculation is performed at the time of transmission;
  A signal distribution measuring step for measuring the signal point distribution of the received signal;
  A residue calculation determination step of comparing the estimation result of the reception signal point distribution with the measurement result of the reception signal point distribution and determining whether to perform a residue calculation on the reception signal;
  A residue calculation step for performing a residue calculation on the received signal when the determination result is a residue calculation;
A communication method comprising:

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