JP6047743B2 - Wireless communication system, wireless communication apparatus, and wireless communication method - Google Patents

Description

  The present invention relates to a radio communication system in which a base station having a plurality of antennas and a terminal device exist, and more particularly, to a radio communication system related to a decoding processing technique in a radio communication system of MIMO (Multiple Input Multiple Output) communication. The present invention relates to a communication system, a wireless communication apparatus, and a wireless communication method.

  In recent years, with the increase in the number of users and the spread of smartphones, the traffic volume of wireless communication systems has increased explosively.

  This trend is expected to accelerate further in the future, and there is an urgent need to significantly improve the traffic capacity of wireless communication systems. Various techniques have been studied for improving the surface frequency utilization efficiency of a wireless communication system, and in particular, the reduction in the number of active users per base station and the propagation loss between the base station (BS) and the mobile terminal (UE). Multi-input multi-output (multi-input multi-output) transmission that improves both the total intra-cell throughput and the throughput of each terminal at the same time, using planar frequency It is expected to be an effective method for improving efficiency.

  Here, the MIMO technology is employed in many communication systems such as a wireless local area network (LAN) (Non-Patent Document 1) and a mobile phone (Non-Patent Document 2) because of its effectiveness. In order to obtain a high effect by the MIMO technology, generally, the correlation between the antenna elements constituting the MIMO is low, and for this purpose, the phase and amplitude can be changed by the propagation path of the signal arriving at each antenna element on the receiving side. It is desirable to be independent only.

  However, in an environment where the transmitting and receiving antennas are visible to each other, the strong direct wave is dominant and the influence of the reflected wave is relatively reduced. Therefore, the diversity of the propagation path is lost and the MIMO effect is reduced. If the cell size is reduced for effective use of frequency in a system such as a mobile phone, the possibility is further increased.

  And as a MIMO technique for a plurality of users, several proposals have already been made for the above-described multi-user MIMO technique (Patent Document 1, Patent Document 2, Patent Document 3). Multi-user MIMO has a large number of antenna elements on the base station (or access point) side and a relatively small number of antenna elements on the terminal side, so that a virtual MIMO channel can be formed simultaneously between the base station and a plurality of terminals. To do.

  In other words, the multi-user MIMO transmission technology is a receiving antenna that transmits independent signals different from each other at the same frequency and same timing from a plurality of transmission antennas to a plurality of communication counterpart devices on the transmission station side and is connected to the plurality of communication counterpart devices. This is a technology that considers the entire system as a huge receiving array and improves simultaneous communication to multiple users and frequency utilization efficiency. In the downlink of a mobile phone system, the number of antenna elements is often limited due to the size of the terminal device, and there is a limit to the spatial multiplexing effect by MIMO, but signals are transmitted to multiple terminal devices at the same frequency and the same time. A downlink MU-MIMO (Multi-User MIMO) system for transmission can achieve a large transmission capacity even in such a situation.

Such a multi-user MIMO technique is also adopted in, for example, LTE (Long Term Evolution) and LTE-A (Long Term Evolution Advanced: LTE). (See Non-Patent Document 3)
As such multi-user MIMO technology, a linear MU-MIMO scheme and a nonlinear MU-MIMO scheme are known.

  In the downlink, the linear MU-MIMO scheme is a technique in which a base station apparatus multiplies a transmission signal by a linear filter (linear precoding) and spatially multiplexes terminal apparatuses.

  On the other hand, examples of the non-linear MU-MIMO system include a VP (Vector Perturbation) MU-MIMO system and a THP (Tomlinson Harashima Precoding) MU-MIMO system (see Non-Patent Document 4 and Patent Document 4).

  That is, as in a general cellular system, in downlink linear multiuser MIMO transmission in a situation where the number of antenna elements of each mobile terminal is smaller than the number of elements of the base station, precoding processing is performed on the base station side, Achieve separation. As this precoding method, an antenna weight is generated based on a zero-forcing (ZF) standard, a minimum mean square error (MMSE) standard, and the like, and is transmitted by multiplying this by a transmission symbol. Examples include spatial filtering (linear precoding).

  Spatial filtering provides a high beamforming gain when the channel correlation between the receiving antennas is small, but the beamforming gain decreases when the channel correlation is large. For this reason, in order to achieve the same transmission performance for each stream, it is necessary to increase the norm of the antenna weight for the stream having a small beamforming gain (that is, to allocate a large transmission power). However, since there is an upper limit on the total transmission power of the transmitter, in such a case, the power efficiency in the transmitter is degraded, causing a decrease in sum-rate (Non-Patent Document 4).

  As one means for overcoming this problem, the vector perturbation method and the THP method, which are a kind of the above-described nonlinear precoding, are attracting attention (Non-patent Documents 4 and 4). For example, in the VP method, an offset vector called a perturbation vector is added to a transmission symbol of each stream in order to suppress an increase in average norm of a transmission signal caused by an antenna weight having a large norm, that is, a decrease in power efficiency. Signal transmission. This perturbation vector is generated so that it can be removed by applying a modulo operation of an appropriate lattice size to the received signal. Specifically, a transmission signal with a perturbation vector added can be obtained by selecting one of the enlarged signal points by using an enlarged signal point arrangement in which normal primary modulation signal points are repeated on the IQ plane at regular intervals. Generate.

  That is, in MU-MIMO using non-linear precoding, MIMO performance degradation is prevented by using the outside of the space where signal points used for digital modulation such as QPSK and QAM are originally arranged.

JP 2005-328312 A JP 2007-110664 A JP 2009-177616 A JP 2011-250073 A

IEEE802.11n Standard 3GPP Standard 36.211 Physical channels and modulation 3GPP Technical Specification 36.211 v8.9.0 Hochwald, B.M. et al., “A vector-perturbation technique for near-capacity multiantenna multiuser communication-part II: perturbation,” IEEE Transactions on Communications, vol.53, no.3, pp. 537-544, March 2005.

  However, since an appropriate value of the modulo lattice size is an unknown value on the receiving side, in such a modulo calculation operation, the boundary between the space where the signal point is originally arranged and the space where the increased signal point exists is present. It is necessary to estimate the distance on the receiving side, and this estimation error causes performance degradation. The estimation error increases as going outward.

  An object of the present invention is to provide a wireless communication system, a wireless communication apparatus, and a wireless communication method capable of reducing the influence of a setting error of a modulo lattice size and improving reception performance in nonlinear MIMO communication. .

  According to an aspect of the present invention, a radio that wirelessly communicates a signal modulated by a predetermined modulation scheme between a first radio communication device and a second radio communication device by a non-linear MIMO (Multiple Input Multiple Output) scheme. In the communication system, the first wireless communication device performs nonlinear precoding and controls antenna directivity based on a plurality of first antennas and a channel state of a transmission path with respect to the second wireless communication device. A precoding unit that executes precoding processing for transmission, and a transmission processing unit for transmitting the output of the precoding unit from a plurality of first antennas using a predetermined modulation scheme, and the second wireless communication apparatus includes: A signal from the second antenna and the first wireless communication apparatus is received by performing demodulation processing for a predetermined modulation method Reception processing unit, a grid position estimation unit that estimates a modulo width for a modulo operation for a signal from the reception processing unit, and estimates a grid position of the signal in the expanded signal point arrangement, and an estimated modulo width A modulo processor that performs modulo operation to remove the influence of the perturbation vector, demodulation processing based on a predetermined constellation for the modulo-calculated signal, and calculation of a weighted likelihood value based on the grid position And a decoding processing unit for performing error correction according to the likelihood value.

  Preferably, the likelihood value weighted based on the lattice position is a likelihood value weighted so as to become smaller as the distance from the origin of the signal point in the enlarged signal point arrangement increases.

  Preferably, the decoding processing unit performs error correction by a soft decision process based on the weighted likelihood value.

  Preferably, the grid position is information indicating how many modulo grids the signal point belongs to from the center point in the enlarged signal point arrangement, and the likelihood value weighted based on the grid position is a predetermined constant. A value having a grid position as a multiplier is used as a weighting factor.

  Preferably, the nonlinear MIMO method is a VP (Vector Perturbation) method.

  According to another aspect of the present invention, a wireless communication apparatus that receives a signal modulated by a predetermined modulation scheme from a base station by a nonlinear MIMO scheme, wherein nonlinear precoding is performed in the nonlinear MIMO scheme, and an antenna A reception processing unit for receiving a signal from the base station by performing demodulation processing for a predetermined modulation method, estimating a modulo width for a modulo operation for the signal from the reception processing unit, and expanding the signal A grid position estimator for estimating a grid position of a signal in a point arrangement, a modulo processor for performing a modulo operation for removing the influence of a perturbation vector by the estimated modulo width, and a predetermined modulo signal Performs demodulation processing based on constellation and calculation of likelihood values weighted based on lattice positions, and performs error correction according to the likelihood values. And a decoding processing unit for.

  Preferably, the likelihood value weighted based on the lattice position is a likelihood value weighted so as to become smaller as the distance from the origin of the signal point in the enlarged signal point arrangement increases.

  Preferably, the decoding processing unit performs error correction by a soft decision process based on the weighted likelihood value.

  Preferably, the grid position is information indicating how many modulo grids the signal point belongs to from the center point in the enlarged signal point arrangement, and the likelihood value weighted based on the grid position is a predetermined constant. A value having a grid position as a multiplier is used as a weighting factor.

  Preferably, the nonlinear MIMO method is a VP method.

  According to still another aspect of the present invention, there is provided a wireless communication method in which a signal modulated by a predetermined modulation method is wirelessly communicated by a nonlinear MIMO method between a first wireless communication device and a second wireless communication device. The first wireless communication apparatus performs non-linear precoding based on the channel state of the transmission path with respect to the second wireless communication apparatus, and executes precoding processing for controlling antenna directivity; A first wireless communication device transmitting a signal after precoding processing from a plurality of first antennas by a predetermined modulation method; and a second wireless communication device from a first wireless communication device to a second antenna. A step of performing demodulation processing for a predetermined modulation scheme and receiving the signal received by the second radio communication device for modulo operation on the demodulated signal; Estimating a modulo width and estimating a lattice position of the signal in the expanded signal point arrangement; and performing a modulo operation for the second wireless communication apparatus to remove the influence of the perturbation vector by the estimated modulo width; The second wireless communication apparatus performs demodulation processing based on a predetermined constellation for the modulo-calculated signal and calculation of a likelihood value weighted based on the lattice position, and according to the likelihood value Performing error correction.

  According to the wireless communication system, the wireless communication apparatus, and the wireless communication method of the present invention, it is possible to improve the reception performance by suppressing the influence of the setting error of the modulo lattice size in the nonlinear MIMO communication.

It is a figure which shows the expansion signal point arrangement | positioning in vector perturbation. It is a figure which shows the influence of the estimation error in an expansion signal point arrangement | positioning as a result of estimating the modulo lattice size by the receiving side. It is a figure explaining the error which arises in a decoding process as a result of having set the wrong modulo boundary by the receiving side. It is a functional block diagram for demonstrating the structure of the radio | wireless communications system 10 of embodiment. 3 is a functional block diagram for explaining a configuration of a signal processor 1204 in a base station 1000. FIG. 3 is a functional block diagram for explaining a configuration of a signal processor 2204 in the mobile terminal 2000. FIG. It is a flowchart for demonstrating the process by the base station side and the mobile station side. It is a figure which shows the relationship between a weighting coefficient and expansion signal point arrangement | positioning. It is a figure which shows the simulation result about QPSK. It is a figure which shows the simulation result about 16QAM.

  Hereinafter, a radio communication system according to an embodiment of the present invention will be described with reference to the drawings. In the following embodiments, components and processing steps given the same reference numerals are the same or equivalent, and the description thereof will not be repeated unless necessary.

  In the following description, the transmission / reception configuration of the MU-MIMO scheme employed in the above-described LTE-Advanced will be described as an example of a basic system configuration. However, the present invention is not limited to this case. Without being limited thereto, the MIMO communication can be applied to a nonlinear MIMO system using modulo arithmetic.

(System operating principle)
First, the operation principle of a general system will be described.

  Thus, in the following, downlink multi-user MIMO transmission with K users is assumed. The number of transmission antennas is Nt, and the number of reception antennas per mobile terminal is Nr. Therefore, the total number of receiving antennas is KNr. Here, it is assumed that Nt = KNr holds, and the transmission data stream number Nd is equal to Nt.

Hereinafter, the description will be given focusing on a single subcarrier. In addition, (•) ^* , (•) ^T and (•) ^H represent a complex conjugate, a transposed matrix, and a complex conjugate transposed matrix, respectively. Further, j is an imaginary unit, and E [·] and | · | ² (vertical double line in the equation) represent an ensemble average and a square Euclidean norm, respectively.

The received signal y = (y ₁ , y ₂ ,... Y _KNr ) ^T is given by the following equation.

Here, z = (z ₁ , z ₂ ,... Z _KNr ) ^T is a transmission signal vector after precoding, H is a channel matrix of size (KNr × Nt), n = (n ₁ , n ₂ ,. n _KNr ) ^T represents an additive white Gaussian noise (AWGN) vector, respectively.
(Vector perturbation (VP))
In the following, it is assumed that vector perturbation using antenna weight based on the MMSE standard is assumed as an example of precoding in nonlinear MIMO. In general transmission spatial filtering, a transmission symbol vector x = (x ₁ , x ₂ ,... X _KNr ) ^T is multiplied by an antenna weight matrix W and transmitted, and an antenna weight matrix W based on the MMSE criterion is given by It is done.

Here, H (tilde) (the one with “˜” on H is described in this way) is a propagation path matrix acquired by the transmitting side by a technique such as propagation path feedback, and I has a size of ( KNr × Nt) unit matrix, γ ₀ represents an average SNR (signal-to-noise ratio) on the receiving side. The transmission signal vector z for spatial filtering is given by the following equation.

Here, P represents average transmission power. From Expression (1) and Expression (3), it can be seen that the received SNR increases as the square Euclidean norm γ _SF of the transmission signal Wx before power normalization decreases.

Therefore, in vector perturbation, a perturbation vector is added to a transmission symbol and transmitted in order to reduce γ _SF . In this case, the perturbation vector needs to be removed on the receiving side without requiring additional information.

  FIG. 1 is a diagram showing an enlarged signal point arrangement in vector perturbation.

In order to realize the vector perturbation processing as described above, as shown in FIG. 1A, on the transmission side, an enlarged signal point obtained by repeating normal primary modulation signal points on the IQ plane at a constant interval τ. Use the arrangement. Then, one point corresponding to the transmission symbol x _i is selected for each stream so that the mean square Euclidean norm of the transmission signal before power normalization is minimized. These are processings for searching for l (tilde) satisfying the following expression (5) (hereinafter, a case where “˜” is added to an English letter is described in this way).

Here, τl (l = (l ₁ ,..., L _Nd ) ^T ) is a perturbation vector corresponding to the difference between the transmission symbol vector on the expanded signal point arrangement and the original transmission symbol vector, and L is the expanded signal point arrangement. It is an integer value indicating the size (perturbation vector search range). As a result, the average square Euclidean norm before power normalization of the transmission signal is expressed by the following equation.

In the following, τ is set so that the minimum signal point distance in the enlarged signal point arrangement is the same as that in the original signal point arrangement. From the above, the transmission signal vector when using VP is expressed by the following equation.

On the receiving side, after compensating the phase error of the received signal due to the precoding error, the influence of the perturbation vector is removed by applying a modulo operation to each element of the received signal as shown in FIG. . The process corresponding to the i-th stream is expressed by the following equation.

Here, g _{i, i} (hat) (the one with “^” on g is expressed as follows. “^” Indicates an estimated value). Represents the post-precoding channel estimation value of i-stream. Finally, symbol demodulation is performed using the received signal y _i ( _tilde ) after removal of the perturbation vector. Note that τ represents the modulo width (modulo lattice size) on the transmission side, and τ ′ represents the modulo width on the reception side.

  Information on the modulo width τ on the transmission side is notified from the transmission side to the reception side at an appropriate timing.

(Modulo grid size setting)
The modulo lattice size τ ′ for removing the perturbation vector is usually set as in the following equation (10) from the relationship of HW˜I.

However, since γ _VP is actually an unknown value on the receiving side, it is necessary to set τ ′ by some method.

For example, it is also possible to set the modulo lattice size based on Equation (11) using the lattice size τ of the expanded signal point arrangement and the post-precoding propagation path estimation value g _{i, i} (hat) of the desired wave component. is there.

However, spatial filtering based on MMSE weights works to allow residual interference and minimize the mean square error from the desired signal point. This means that the received power of the desired wave component is smaller than the power of the signal actually received. For this reason, the modulo lattice size τ ′ (hat) set by using the precoding propagation path estimation value g _{i, i} (hat) of the desired wave component is smaller than the value of Expression (10) which is a desired value. It tends to be a value.

  Although there are other proposals for estimating the estimated value τ ′ (hat) of the modulo lattice size, there is no change in the existence of an estimation error.

  Further, as shown in FIG. 1B, performing the process of returning the received signal point from the expanded signal point arrangement to the original signal point arrangement by such a modulo operation also affects the likelihood of the signal point. give.

  In other words, in the VP method and the THP method, there are a case where the original transmission symbol is transmitted as it is and a case where the transmission symbol is transmitted at any one of the signal points expanded with τ as the lattice size. Conventionally, on the receiving side, after returning to the original signal point by modulo calculation using τ ′ as the lattice size, the likelihood value (LLR value) is obtained from the least square distance to the candidate point that would have been transmitted. At this time, the calculation of the likelihood value is the same regardless of which enlarged signal point is used.

  However, in actuality, in the modulo operation, it is necessary to estimate the distance to the boundary between the space where the signal point is originally placed and the space where the increased signal point exists, and this estimation error estimation error is The bigger you go, the bigger it becomes. Therefore, it is originally necessary to calculate the likelihood in consideration of the position in the enlarged signal point arrangement.

  Therefore, in the present embodiment, as shown in FIG. 1B, the likelihood value of the received signal point is calculated in consideration of the position information in the enlarged signal point arrangement.

  FIG. 2 is a diagram illustrating the influence of an estimation error in an enlarged signal point arrangement as a result of estimating the modulo lattice size on the receiving side.

  Since the grid size of the modulo operation is unknown on the receiving side, it must be calculated from the propagation path estimation value. A grating size setting error is also caused by the propagation path estimation error.

  As shown in FIG. 2, when the estimated value τ ′ (hat) of the modulo lattice size on the receiving side is smaller than the original modulo lattice size, the error between the correct modulo boundary and the incorrect modulo boundary is the enlarged signal point. In the arrangement, the distance from the origin increases. Conversely, the same applies when the estimated value τ ′ (hat) of the modulo lattice size is larger than the original modulo lattice size.

  Accordingly, when the outer enlarged signal point is used, the probability is further lowered, and it is necessary to consider such a situation also in the likelihood value calculation.

  FIG. 3 is a diagram for explaining an error that occurs in the decoding process as a result of setting an incorrect modulo boundary on the receiving side.

  The process of returning the signal point from the enlarged signal point arrangement to the original signal point arrangement by modulo calculation is referred to as “remapping by modulo calculation”.

  In FIG. 3, such an error is emphasized for explanation.

  Since the estimated value τ ′ (hat) of the modulo lattice size on the receiving side is smaller than the original modulo lattice size, the signal point farther from the origin in the enlarged signal point arrangement on the receiving side is modulo-calculated. It can be seen that the remapping by remapping is performed at a position that is significantly different from the original symbol position.

  Therefore, in the present embodiment, processing for weighting the likelihood value of the signal point is performed by a method described in more detail below.

(Outline of wireless communication system)
FIG. 4 is a functional block diagram for explaining a specific configuration of radio communication system 10 of the present embodiment.

  In FIG. 4, the number of users is K = 4, the number of transmission antennas is Nt = 8, and the number of reception antennas per mobile terminal is Nr = 2.

  Referring to FIG. 4, base station 1000 on the transmission side includes a signal processing unit 1200 that performs processing such as encoding a transmission signal as a digital signal, and a high-frequency signal by converting the encoded signal into an analog signal. And RF processing section 1100 for transmitting from antennas 1002-1 to 1002-8.

  Here, FIG. 4 shows an 8 × 8 MIMO configuration with one base station and four mobile terminals (mobile stations) as an example, and the base station 1000 is provided with eight antennas. The number of base station antennas, the number of mobile stations, and the number of mobile station antennas are not limited to such numbers.

  In FIG. 4, signal transmission between the RF processing unit 1100 and the signal processing unit 1200 is performed by optical communication. The signal transmission method is not limited to optical communication. For example, the RF processing unit 1100 and the signal processing unit 1200 are housed in one housing, and signals are transmitted and received by electrical signals. There may be.

  In base station 1000, RF processing section 1100 also performs reception processing for down-converting signals received by antennas 1002-1 to 1002-8 and converting them into digital signals, and signal processing section 1200 performs RF processing. Processing such as decoding the signal from the processing unit 1100 as a digital signal is also performed.

  That is, the RF processing unit 1100 is provided corresponding to each of the antennas 1002-1 to 1002-8, and functions as a front end for transmitting and receiving a high-frequency signal. The RF unit 1102-1 to 1102-8 and the RF unit 1102-1 A / D and D / A converters 1104-1 to 1104-8, which are provided corresponding to each of .about.1102-8, convert the transmission signal into digital / analog, and convert the reception signal into analog / digital, and a signal processing unit. 1200 and optical interface (optical I / F) units 1106-1 to 1106-8 for transmitting and receiving signals through optical communication.

  The signal processing unit 1200 includes optical I / F units 1202-1 to 1202-8 and optical I / F units 1202-1 to 1202-8 for transmitting and receiving signals to and from the RF processing unit 1100, respectively. Correspondingly, signal processors 1204-1 to 1204-8 are provided for executing digital signal processing for encoding transmission signals and decoding reception signals.

  The configuration of the signal processors 1204-1 to 1204-8 will be described later.

  On the other hand, mobile terminals 2000-1 to 2000-4 on the receiving side (hereinafter referred to as mobile terminal 2000 when mobile terminals need to be collectively referred to) have basically the same configuration. Hereinafter, the configuration of mobile terminal 2000-1 will be described.

  The mobile terminal 2000-1 has a signal processing unit 2200-1 that performs processing such as encoding a transmission signal as a digital signal, and converts the encoded signal into an analog signal and up-converts the signal into a high-frequency signal. And an RF processing unit 2100-1 for transmitting from the antennas 2002-1 to 2002-2. Also in the mobile terminal 2000-1, the RF processing unit 2100-1 also performs a reception process of down-converting a signal received by the antennas 2002-11 to 2002-12 and converting the signal into a digital signal. 2200-1 also performs processing such as decoding processing of the signal from the RF processing unit 2100-1 as a digital signal.

  In FIG. 4, as an example, also in the mobile terminal 2000-1, the signal transmission between the RF processing unit 2100-1 and the signal processing unit 2200-1 is performed by optical communication.

  Similarly to the base station 1000 side, the RF processing unit 2100-1 is provided corresponding to each of the antennas 2002-11 to 2002-12, and functions as a front end for transmitting and receiving high-frequency signals. -12 and RF units 1102-11 to 1102-12, A / D and D / A converters 2104-11 for converting the transmission signals from digital to analog and converting the received signals from analog to digital, respectively. To 2104-12, and a signal processing unit 1200, and optical I / F units 2106-11 to 2106-12 for exchanging signals through optical communication, respectively.

  The signal processing unit 2200-1 includes optical I / F units 2202-11 to 2202-12 and optical I / F units 2202-11 to 2202 for transmitting and receiving signals to and from the RF processing unit 2100-1, respectively. -12 and signal processors 2204-11 to 2204-12 for executing digital signal processing of transmission signal encoding and reception signal decoding.

The configuration of the signal processors 2204-11 to 2204-12 will be described later.
(Configuration of transmitter signal processor)
FIG. 5 is a functional block diagram for explaining a configuration of a signal processor 1204 in the base station 1000 (hereinafter, the signal processors 1204-1 to 1204-8 are collectively referred to as the signal processor 1204).

  In the following description, orthogonal frequency division multiplexing (OFDM) using multicarriers will be described as an example, but the above-described perturbation vector addition processing can also be applied to a single carrier.

  Referring to FIG. 5, the signal processor 1204 includes an OFDM demodulator 1210 that performs demodulation processing (hereinafter referred to as “OFDM demodulation processing”) on the received data with respect to the OFDM modulation scheme. In the RE demapper unit 1212, the resource element is demapped. The demapped information includes the reference signal C-RS.

  The uplink channel evaluation unit 1214 acquires channel state information CSI using the reference signal C-RS.

  The signal separation unit 1216 weights the signal from each antenna with reference to the channel state information CSI, and separates a desired signal from a plurality of systems of signals. After being demapped to a signal corresponding to each stream by the layer demapping unit 1218, the demodulating unit 1220 demodulates, for example, a signal that has been modulated into QAM. The signal descrambled by the descrambling processing unit 1222 is subjected to processing such as error detection and error correction by the channel decoding unit 1224.

  The feedback information extraction unit 1226 extracts feedback information for specifying a weight matrix selected as an appropriate precoding weight based on a predetermined criterion from the channel-decoded signal.

  For example, the channel coding unit 1230 performs coding for error detection and error correction on the data to be transmitted, and after the scramble processing unit 1232 performs the scramble processing, the modulation unit 1234 converts the transmission symbol into a constellation. A modulation process corresponding to a predetermined signal point, for example, a QAM modulation process is executed.

  The pre-encoding unit 1240 performs “enlargement” on the signal obtained by mapping the plurality of streams by the layer mapping unit 1236 and the reference signal DM-RS for channel estimation generated by the reference signal generation unit 1238 as described in FIG. Based on the “signal point arrangement”, perturbation vectors in the VP method are added and precoding processing is performed.

  Further, the reference signal C-RS, CSI-RS, and the synchronization signal for channel quality evaluation on the terminal side generated by the reference signal generation unit 1238 are mapped to the resource element by the RE mapper 1242 after the precoding. After that, the OFDM modulation unit 1244 performs modulation processing as an OFDM signal.

In addition, in the precoding process performed by the precoding unit 1240, the perturbation vector addition process executed based on the “enlarged signal point arrangement” in FIG. 1 is as described above.
(Receiver side signal processor configuration)
FIG. 6 is a functional block diagram for explaining the configuration of the signal processor 2204 (hereinafter, the signal processors 2204-11 to 2204-42 are collectively referred to as the signal processor 2204) in the mobile terminal 2000.

  Referring to FIG. 6, signal processor 1204 has a frame synchronization unit 2206 for performing frame synchronization with a pilot signal of received data, and an OFDM demodulation process based on the timing generated by frame synchronization unit 2206 for the received data The demodulated signal is demapped to resource elements in the RE demapper unit 2207. The demapped information includes the reference signal CSI-RS and the reference signal DM-RS.

  The downlink channel evaluation unit 2220 estimates a propagation path using the reference signal CSI-RS, and acquires channel state information CSI, noise power, signal power, and the like. On the other hand, the tau evaluation unit 2208 calculates a post-coding channel estimation value from the reference signal DM-RS demapped by the RE demapper 2206, and, for example, the modulo width in the modulo operation by the above-described equation (11). To evaluate.

  The lattice position estimation processing unit 2209 estimates the lattice position according to the following equation (12).

That is, the lattice position l (tilde) indicates to which lattice the I component or the Q component belongs with respect to the origin in the enlarged signal point arrangement. More generally, the lattice position is “a value representing the distance from the origin of the signal point in the enlarged signal point arrangement”. Therefore, the method of calculating the value of the lattice position is not necessarily limited to the above-described method.

  The information on the lattice position estimated in this way may be added as an additional bit to the information on the signal point, for example, so that it can be used in the weighting process for the later likelihood calculation. Alternatively, other configurations may be used as long as the information on the lattice position can be used in the weighting process for the later likelihood calculation.

  The modulo processing unit 2210 performs a modulo operation based on the evaluated modulo width.

  Here, the reference signal CSI-RS is used to obtain information on “primary propagation path” in order to calculate precoding weights, and the reference signal DM-RS demodulates a precoding signal. In order to do this, it is for acquiring information about “propagation path after precoding”.

  After the modulo operation is performed, the layer demapping 2212 performs demapping processing to each layer, and then the demodulator 2214 demodulates, for example, a signal that has been QAM modulated. At this time, a likelihood value (or a log likelihood value LLR) may be calculated for each signal point.

  The demodulated signal is descrambled by a descrambling processing unit 2216.

  For the descrambled signal, the weighting processing unit 2215 weights the likelihood value associated with each signal point using the information on the grid position as follows.

FIG. 8 is a diagram showing the relationship between such weighting coefficients and enlarged signal point arrangement.

  As shown in FIG. 8, in the enlarged signal point arrangement, the value of the weighting coefficient βm decreases as the distance from the origin increases.

  That is, more generally, the “weight” added to the likelihood value may be “a weight that becomes smaller as the distance from the origin of the signal point in the enlarged signal point arrangement increases”, and is not necessarily described above. The configuration is not limited to the above.

  Channel decoding section 2218 performs processing such as error detection and error correction on the weighted signal. At this time, error detection / error correction is executed using the weighted likelihood value. Although not particularly limited, for example, it can be used as a likelihood value of an input signal when soft decision is used as in the decoding process of a turbo code.

  The feedback information insertion unit 2222 generates channel state information to be fed back according to the evaluation result in the downlink channel evaluation unit 2220.

  For example, the channel encoding unit 2224 performs encoding for error detection / error correction on the data to be transmitted, and after the scramble processing unit 2226 performs the scramble processing, the modulation unit 2228 converts the transmission symbol into a constellation. A modulation process corresponding to a predetermined signal point, for example, a QAM modulation process is executed.

  A signal obtained by mapping a plurality of streams by the layer mapping unit 2230, a reference signal DM-RS for channel estimation generated by the reference signal generation unit 2232, reference signals C-RS, CSI-RS for channel quality evaluation, a synchronization signal, and the like After being mapped to resource elements by the RE mapper 2234, the OFDM modulation unit 2236 performs modulation processing as an OFDM signal.

  FIG. 7 is a flowchart for explaining the processes on the base station side and the mobile station side described above.

  In FIG. 7, the base station 1000 is the transmitting side, and the mobile terminal 2000 is the receiving side.

  Referring to FIG. 7, in base station 1000 on the transmission side, a weight matrix of MMSE is calculated based on channel state information fed back from the reception side (S100), and perturbation added based on the MMSE weight matrix Vector calculation processing is executed (S102).

  Further, the signal added with the perturbation vector is multiplied by the MMSE weight matrix and transmitted from the antennas 1002-1 to 1002-8 (S104).

  In the mobile terminal 2000 on the receiving side, the propagation path is estimated by the reference signal CSI-RS extracted from the signal after OFDM demodulation, and channel state information fed back to the transmitting side is generated (S110).

  Further, the tau evaluation unit 2208 of the mobile terminal 2000 on the receiving side performs a modulo width estimation process using the reference signal DM-RS (S112).

  Subsequently, the lattice position estimation processing unit 2209 estimates the lattice position according to Expression (12) (S114).

  Subsequently, the mobile terminal 2000 on the receiving side performs a modulo operation on the signal after OFDM demodulation (S116), and further executes a demodulation process and a likelihood value calculation process in the demodulation unit 2214 (S118). The weighting process for the likelihood value of the signal point is executed by the weighting processing unit 2215 (S120). Further, after descrambling processing, channel detection section 2218 performs processing such as error detection and error correction by soft decision processing using the weighted likelihood values (S122).

  On the other hand, the receiving-side mobile terminal 2000 feeds back the estimated channel state information to the transmitting-side base station 1000 (S124).

The information fed back to the transmission side may be the channel state information itself as described above, or information for specifying a weight matrix selected as appropriate on the terminal side according to the channel state information. It may be.
(Computer simulation)
(simulation result)
FIG. 9 is a diagram illustrating simulation results for QPSK.

  The coding rate R was set to 3/4, and the WINNER II A1 LOS model was used for the propagation path model in consideration of the indoor office environment with a view.

  Here, the WINNER II A1 LOS model is disclosed below.

“WINNER II channel models, Part I Channel models” IST-4-027756 WINNER II, D1.1.2 V1.2, Feb. 2008.
The conditions of this simulation are as follows: 8 base station antennas, 2 mobile station antennas, 4 mobile stations, error correction: Turbo decoding (MAX Log-MAP, 6 decoding repetitions, interleaver length 6144 @ QPSK, 5120 @ 16QAM ).

Compared to the conventional method (α = 1), the required SNR of BER = 10 ⁻² is improved by about 1.5 dB.

  FIG. 10 is a diagram illustrating simulation results for 16QAM.

  The simulation conditions are the same as in FIG.

Compared to the conventional method (α = 1), the required SNR of BER = 10 ⁻² is improved by about 1.0 dB.

  As described above, according to the radio communication system, radio communication apparatus, and radio communication method of the present embodiment, it is possible to improve the reception performance by reducing the influence of the setting error of the modulo lattice size in the nonlinear MIMO communication. Is possible.

  In the above description, the present invention has been mainly described by taking the VP method as a specific example. However, the present invention is not limited to such a configuration, and nonlinear precoding is performed on the transmission side, and the reception side is configured. As long as the communication method executes a modulo operation for removing the influence of the perturbation vector, it can be applied to other communication methods.

  Embodiment disclosed this time is an illustration of the structure for implementing this invention concretely, Comprising: The technical scope of this invention is not restrict | limited. The technical scope of the present invention is shown not by the description of the embodiment but by the scope of the claims, and includes modifications within the wording and equivalent meanings of the scope of the claims. Is intended.

  10 wireless communication system, 1000 base station, 1002-1 to 1002-8 antenna, 1100 RF processing unit, 1200 signal processing unit, 1102-1 to 1102-8 RF unit, 1104-1 to 1104-8 A / D and D / A conversion unit, 1204-1 to 1204-8 signal processor, 1240 precoding unit, 2000-1 to 2000-4 mobile terminal, 2002-11 to 2002-12 antenna, 2100-1 RF processing unit, 2102-11 2102-12 RF unit, 2104-11 to 2104-12 A / D and D / A conversion unit, 2200-1 signal processing unit, 2204-11 to 2204-12 signal processor, 2208 tau evaluation unit, 2209 lattice position estimation processing Unit, 2210 modulo processing unit, 2214 demodulation unit, 2215 weighting Processing section, 2216 descramble processing section, 2218 the channel decoding unit.

Claims (11)

A wireless communication system that performs wireless communication between a first wireless communication device and a second wireless communication device using a non-linear MIMO (Multiple Input Multiple Output) method, a signal modulated by a predetermined modulation method,
The first wireless communication device is:
A plurality of first antennas;
A precoding unit that performs non-linear precoding and performs precoding processing for controlling antenna directivity based on a channel state of a transmission path for the second wireless communication device;
A transmission processing unit for transmitting the output of the precoding unit from the plurality of first antennas by the predetermined modulation scheme;
The second wireless communication device is:
A second antenna;
A reception processing unit for receiving a signal from the first wireless communication apparatus by executing demodulation processing for the predetermined modulation method;
With respect to the signal from the reception processing unit, a modulo width for modulo calculation is estimated, and a lattice position estimation unit that estimates a lattice position of the signal in the expanded signal point arrangement;
A modulo processing unit for performing a modulo operation for removing the influence of a perturbation vector by the estimated modulo width;
A demodulation process based on a predetermined constellation for the modulo-calculated signal and a calculation of a likelihood value weighted based on the lattice position, and error correction is performed according to the likelihood value A wireless communication system comprising a decoding processing unit.   The likelihood value weighted based on the lattice position is a likelihood value weighted so as to become smaller as the distance from the origin of the signal point in the enlarged signal point arrangement increases. Wireless communication system.   The wireless communication system according to claim 2, wherein the decoding processing unit performs the error correction by a soft decision process based on the weighted likelihood value. The grid position is information indicating how many modulo grids the signal point belongs to from the center point in the enlarged signal point arrangement,
The wireless communication system according to claim 2, wherein the likelihood value weighted based on the lattice position uses a value obtained by multiplying a predetermined constant by the lattice position as a weighting factor.   The wireless communication system according to claim 1, wherein the nonlinear MIMO scheme is a VP (Vector Perturbation) method. A wireless communication apparatus that receives a signal modulated by a predetermined modulation scheme from a base station by a nonlinear MIMO scheme,
In the nonlinear MIMO system, nonlinear precoding is performed,
An antenna,
A reception processing unit for receiving a signal from the base station by executing a demodulation process for the predetermined modulation scheme;
With respect to the signal from the reception processing unit, a modulo width for modulo calculation is estimated, and a lattice position estimation unit that estimates a lattice position of the signal in the expanded signal point arrangement;
A modulo processing unit for performing a modulo operation for removing the influence of a perturbation vector by the estimated modulo width;
A demodulation process based on a predetermined constellation for the modulo-calculated signal and a calculation of a likelihood value weighted based on the lattice position, and error correction is performed according to the likelihood value A wireless communication apparatus comprising: a decoding processing unit.   The likelihood value weighted based on the grid position is a likelihood value weighted so as to become smaller as the distance from the origin of the signal point in the enlarged signal point arrangement increases. Wireless communication device.   The radio communication apparatus according to claim 7, wherein the decoding processing unit performs the error correction by a soft decision process based on the weighted likelihood value. The grid position is information indicating how many modulo grids the signal point belongs to from the center point in the enlarged signal point arrangement,
The wireless communication apparatus according to claim 7, wherein the likelihood value weighted based on the lattice position is a weight coefficient that is a value that is a multiplier of the lattice position with respect to a predetermined constant.   The wireless communication apparatus according to claim 6, wherein the nonlinear MIMO method is a VP method. A wireless communication method for wirelessly communicating a signal modulated by a predetermined modulation method by a nonlinear MIMO method between a first wireless communication device and a second wireless communication device,
The first wireless communication apparatus performs nonlinear precoding based on a channel state of a transmission path with respect to the second wireless communication apparatus, and executes a precoding process for controlling antenna directivity;
The first wireless communication apparatus transmitting the pre-coded signal from a plurality of first antennas by the predetermined modulation method;
The second wireless communication apparatus receiving a signal received by the second antenna from the first wireless communication apparatus by performing a demodulation process for the predetermined modulation method;
The second wireless communication apparatus estimating a modulo width for a modulo operation with respect to the demodulated signal, and estimating a lattice position of a signal in an expanded signal point arrangement;
The second wireless communication apparatus performing a modulo operation for removing the influence of a perturbation vector by the estimated modulo width;
The second wireless communication device performs a demodulation process based on a predetermined constellation for the modulo-calculated signal, and calculates a likelihood value weighted based on the lattice position, and the likelihood value And a step of performing error correction according to the method.