JP5777092B2 - Wireless communication device, wireless transmission system, and wireless transmission method - Google Patents

Description

  The present invention relates to a wireless communication device, a wireless transmission system, and a wireless transmission control method.

  2. Description of the Related Art Conventionally, a MIMO (Multi Input Multi Output) wireless transmission system that transmits and receives data with a plurality of antennas is known. This MIMO radio transmission system is adopted in the LTE (Long Term Evolution) communication standard defined by 3GPP (Third Generation Partnership Project), which is a standardization project for third generation (3G) mobile communication systems, and is also LTE- Adoption is also being studied in the Advanced communication standard. In a mobile communication system that employs a MIMO wireless transmission scheme, a base station device (eNode-B) that is one of the plurality of wireless communication devices that perform data transmission and reception and a mobile station that is the other wireless communication device (eNode-B) By performing data transmission / reception with a plurality of different transmission layers (streams) using a plurality of antennas with a UE (user equipment), wireless transmission by a MIMO spatial multiplexing scheme or a MIMO diversity scheme can be performed. The MIMO spatial multiplexing scheme is a scheme in which different signals are transmitted in parallel from a plurality of antennas using the same radio resource (frequency and time), and the MIMO diversity scheme is the same signal transmitted from a plurality of antennas in space-time (or , Space-frequency) transmission. In LTE / LTE-Advanced, precoding is applied on the transmission side for both the MIMO spatial multiplexing method and the MIMO diversity method, but the open-loop type (Open-Loop MIMO) and reception that do not use feedback control from the reception side. There is a closed loop type (Closed-Loop MIMO) using feedback information from the side (see Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3).

  In the above MIMO radio transmission system, the number of transmission layers (also called “spatial multiplexing number” or “rank”) is set according to channel conditions such as reception SINR (Signal-to-Interference and Noise power Ratio) and fading correlation between antennas. Rank adaptation control for adaptive control is applied. When the number of transmission layers is 1, it corresponds to the MIMO diversity scheme, and when the number of transmission layers is two or more, it corresponds to the MIMO spatial multiplexing scheme. Therefore, rank adaptation control corresponds to control for adaptively switching between the MIMO diversity scheme and the MIMO spatial multiplexing scheme depending on the channel state. In order to apply this rank adaptation control, the mobile station (UE) on the reception side transmits appropriate transmission to the base station (eNode-B) on the transmission side in addition to channel quality information (CQI: Channel Quality Indicator). The base station dynamically controls the number of transmission layers by feeding back rank information (RI: Rank Indicator) related to the number of layers (see Non-Patent Document 4).

  Further, for example, in Patent Document 1, the base station (eNode-B, transmission side) uses the uplink for rank information RI determined by the mobile station (UE, reception side) for LTE downlink. And the obtained rank information RI is adjusted using an offset value unique to the mobile station, and the number of streams used for simultaneous transmission to the mobile station (number of transmission layers) based on the adjusted rank information RI Is disclosed.

The rank information RI is preferably generated according to the state of the radio transmission path such as reception SINR on the reception side and fading correlation between transmission antennas and reception antennas. For example, if the received SINR is high and the fading correlation between transmitting antennas and receiving antennas is low, the number of transmission layers is increased because it is suitable for the MIMO radio transmission system, and in other cases, the number of transmission layers is decreased. Next, rank information RI is generated. By the way, the radio transmission characteristics (throughput characteristics) of the MIMO radio transmission system generally depend not only on the state of the radio propagation path but also on reception algorithms such as channel estimation and multiple signal separation, and the influence is particularly significant in MIMO spatial multiplexing. On the other hand, it is known that the influence is relatively small in MIMO diversity. For example, in MIMO spatial multiplexing, Maximum Likelihood Detection (MLD), which is known as an optimal multiple signal separation method, has good signal separation accuracy even in a propagation environment having a low reception SINR and a high fading correlation. Therefore, there are relatively many places where throughput higher than MIMO diversity can be obtained. On the other hand, in the most common minimum mean square error (MMMSE) detection as the multiple signal separation, the signal separation accuracy is significantly deteriorated in a propagation environment having a low reception SINR or a high fading correlation. In such an environment, MIMO diversity often provides higher throughput than MIMO spatial multiplexing using MMSE for multiple signal separation. Therefore, the optimal number of transmission layers depends not only on the state of the radio propagation path but also on reception algorithms such as channel estimation and multiple signal separation. In general, the number of transmission layers is determined according to rank information RI fed back from the reception side. Therefore, it is necessary to generate an optimal RI in order to maximize the throughput in the MIMO radio transmission system to which rank adaptation control is applied. For this purpose, it is necessary to generate the rank information RI in consideration of the fact that radio transmission characteristics vary greatly depending on the type of reception algorithm.
In the base station apparatus disclosed in Patent Document 1, the mobile station (UE) moves on the receiving side in order to reduce degradation of desired radio transmission characteristics in rank adaptation control due to measurement error of the radio transmission path state in the mobile station (UE). A method of correcting the rank information RI generated on the station (UE) side based on the actual transmission error rate measurement result on the base station side serving as the transmission side is shown. A specific method for generating the optimum value of the rank information RI on the side is not shown. For this reason, since the optimal rank information RI cannot be generated, there is a possibility that the wireless transmission characteristic (throughput characteristic) is deteriorated.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a wireless communication apparatus that can easily generate optimal rank information by absorbing differences in wireless transmission characteristics depending on the type of reception algorithm. It is to provide a wireless transmission system and a wireless transmission control method.

In order to achieve the above object, a first aspect of the present invention is a wireless transmission system that transmits and receives data using a plurality of different transmission layers between a plurality of wireless communication devices, wherein the plurality of wireless communication devices are configured to transmit and receive data. A plurality of singular values of a MIMO channel matrix or a plurality of eigenvalues of a correlation matrix of the MIMO channel matrix indicating transmission characteristics of a MIMO channel between the plurality of wireless communication devices based on reception results of known pilot signals transmitted and received Calculating means for calculating the interference noise level in the MIMO channel based on the reception result of the known pilot signal, and setting the threshold based on the estimation result of the interference noise level Based on a comparison result between the threshold setting means, the plurality of singular values or the plurality of eigenvalues, and the threshold, And rank information generating means for generating a rank information indicating the number of transmission layers used for data transmission and reception in the IMO channel and is characterized in that it comprises.
Further, the invention according to claim 2 is the wireless transmission system according to claim 1, wherein the rank information generating means is a value obtained by squaring the plurality of singular values or the plurality of the plurality of singular values when the maximum number of transmission layers of the MIMO channel is two. A minimum value is obtained for the eigenvalues, and when the minimum value is greater than or equal to the threshold value or greater than the threshold value, the optimum number of transmission layers is set to two.
The invention according to claim 3 is the wireless transmission system according to claim 1 or 2, wherein the threshold value is obtained by offsetting the interference noise level by a preset offset amount and normalizing with the total transmission power of the pilot signal. It is characterized by being.
According to a fourth aspect of the present invention, in the wireless transmission system according to the first, second, or third aspect, transmission / reception between the plurality of wireless communication devices is performed using a plurality of subcarriers, and the calculation means A value obtained by squaring a plurality of singular values of the MIMO channel matrix or a correlation matrix of the MIMO channel matrix based on reception results of known pilot signals by each of the plurality of subcarriers transmitted and received between the wireless communication apparatuses For each of the plurality of eigenvalues, an average value between the plurality of subcarriers is calculated, and the interference noise level estimation means determines the MIMO based on a reception result of a known pilot signal by each of the plurality of subcarriers. An interference noise level in the channel is estimated, and the rank information generating means is a mean square value of the plurality of singular values or the plurality of singular values. The average value of the eigenvalues of, based on a result of comparison between the threshold value, is characterized in that to generate the rank information of the MIMO channel.
According to a fifth aspect of the present invention, in the wireless transmission system according to the first, second, third, or fourth aspect, the average value is an average obtained by weighting the plurality of subcarriers. Is.
The invention according to claim 6 is the wireless transmission system according to claim 1, 2, 3, 4 or 5, wherein the plurality of wireless communication devices include a wireless communication device on a data transmission side for transmitting data, and the data. The data receiving side wireless communication apparatus includes the calculation means, the interference noise level estimating means, the threshold setting means, and the rank information generating means. Both of them further comprise rank information transmitting means for transmitting the rank information generated by the rank information generating means to the wireless communication apparatus on the data transmitting side, and the wireless communication apparatus on the data transmitting side transmits the rank information to the data Rank information receiving means for receiving from the receiving-side wireless communication device, and the number of transmission rays indicated by the rank information based on the rank information by the rank information receiving means. Is characterized in further comprising data transmission means for transmitting data to the wireless communication apparatus of the data receiving side, a by.
The invention according to claim 7 is a wireless communication apparatus on a data receiving side that receives the data in a wireless transmission system that transmits and receives data by a plurality of different transmission layers between the plurality of wireless communication apparatuses, A plurality of singular values of a MIMO channel matrix indicating transmission characteristics of a MIMO channel between the plurality of wireless communication devices based on reception results of known pilot signals transmitted / received between the plurality of wireless communication devices or the MIMO channel matrix A calculation means for calculating a plurality of eigenvalues of the correlation matrix, an interference noise level estimation means for estimating an interference noise level in the MIMO channel based on a reception result of the known pilot signal, and an interference noise level estimation means After offsetting the estimated interference noise level by a predetermined offset amount, Threshold value setting means for setting a threshold value based on interference noise level, and the number of transmission layers used for data transmission / reception in the MIMO channel based on a comparison result between the plurality of singular values or the plurality of eigenvalues and the threshold value Rank information generating means for generating rank information; and rank information transmitting means for transmitting the rank information generated by the rank information generating means to the wireless communication device on the data transmitting side. is there.
The invention of claim 8 is a wireless transmission method for transmitting and receiving data by a plurality of different transmission layers between a plurality of wireless communication devices, and is a known pilot transmitted and received between the plurality of wireless communication devices. Calculating a plurality of singular values of a MIMO channel matrix indicating a transmission characteristic of a MIMO channel between the plurality of wireless communication devices or a plurality of eigenvalues of a correlation matrix of the MIMO channel matrix based on a signal reception result; Based on the reception result of the known pilot signal, estimating the interference noise level in the MIMO channel, offset the estimated interference noise level by a predetermined offset amount, and based on the interference noise level after the offset Setting a threshold value, the plurality of singular values or the plurality of eigenvalues, and the threshold value And generating rank information indicating the number of transmission layers used for data transmission / reception in the MIMO channel, and data between the plurality of wireless communication devices by the number of transmission layers indicated by the rank information. The step of performing transmission / reception of is included.

In the present invention, based on reception results of known pilot signals transmitted / received between a plurality of wireless communication apparatuses, a plurality of unique MIMO channel matrices indicating transmission characteristics of a MIMO channel between the plurality of wireless communication apparatuses. Or a plurality of eigenvalues of the correlation matrix of the MIMO channel matrix. The calculated number of eigenvalues or singular values is the maximum number of virtual SISO (Single Input Single Output) channels obtained by decomposing the MIMO channels so that they are independent of each other in parallel, that is, independently of each other. This corresponds to the maximum number of transmission layers that can transmit data. Each of the calculated plurality of eigenvalues or the plurality of singular values corresponds to a transmission gain of a transmission path formed in the SISO channel, that is, a transmission layer. Here, if an eigenvalue or a singular value having a value larger than a predetermined threshold value is selected and a transmission layer corresponding to the selected eigenvalue or singular value is used, data is transmitted only by a transmission layer having a predetermined transmission gain. Since data is transmitted, the data capacity that can be transmitted by the MIMO channel can be brought close to the theoretical capacity limit (Shannon capacity). Therefore, by generating rank information indicating the number of transmission layers used for data transmission / reception in the MIMO channel based on a comparison result between the plurality of eigenvalues or the plurality of singular values and a predetermined threshold, It is possible to generate optimum rank information that can bring the data capacity that can be transmitted and received close to the theoretical capacity limit (Shannon capacity).
Moreover, in the present invention, based on the reception result of the known pilot signal, the interference noise level reflecting the state of the radio transmission path in the MIMO channel is estimated, and based on the estimation result of the interference noise level, the above-mentioned A threshold value to be compared with a plurality of eigenvalues or the plurality of singular values is set. This threshold value reflects the state of the radio transmission path in the MIMO channel, and can be arbitrarily adjusted by simple processing such as changing according to the type of reception algorithm. Then, the threshold value thus set is compared with the plurality of eigenvalues or the plurality of singular values, and rank information indicating the number of transmission layers used for data transmission / reception in the MIMO channel is generated based on the comparison result. Yes. Therefore, not only can it adapt to changes in the state of the wireless transmission path such as reception SINR and fading correlation, but it can also generate rank information by absorbing differences in wireless transmission characteristics (throughput characteristics) that depend on the type of reception algorithm. .
As described above, according to the present invention, it is possible to absorb the difference in radio transmission characteristics depending on the type of reception algorithm and easily generate optimal rank information.

The functional block diagram which shows an example of schematic structure of the radio base station and user apparatus in the downlink of the closed-loop type MIMO radio transmission system which concerns on one Embodiment which can apply this invention. The functional block diagram which shows an example of schematic structure of the radio base station and user apparatus in the downlink of the open loop type MIMO wireless transmission system which concerns on other embodiment which can apply this invention. The functional block diagram which shows an example of schematic structure of the radio base station and user apparatus in the uplink of the closed-loop type | mold MIMO radio | wireless transmission system which concerns on other embodiment which can apply this invention. The schematic diagram which shows each element of the MIMO channel matrix which carried out equivalent conversion of the transmission path between a radio base station and a user apparatus. The schematic diagram which shows the equivalent circuit of a MIMO channel matrix in the equivalent conversion of a MIMO channel matrix. The schematic diagram which shows the notation of the channel matrix in a SVD-MIMO transmission model. The schematic diagram which shows the notation of the channel matrix in a SVD-MIMO transmission equivalent model. Explanatory drawing of the setting of the rank information RI based on the average eigenvalue and threshold value (beta) in the case where the number M of equivalent transmission paths is an arbitrary number. Explanatory drawing of the setting of the rank information RI based on the average eigenvalue and threshold value (beta) in case the number M of equivalent transmission paths is two.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the overall configuration of a MIMO wireless transmission system to which the present invention can be applied will be described.
FIG. 1 is a functional block diagram illustrating an example of a schematic configuration of a radio base station and a user apparatus in a downlink of a closed-loop MIMO radio transmission system according to an embodiment to which the present invention can be applied. The MIMO radio transmission system shown in FIG. 1 is based on control information (PMI: Precoding Matrix Indicator) that is an index of a candidate data table (codebook) of an optimal transmission antenna weight matrix fed back from the user apparatus 10. This is a closed-loop MIMO wireless transmission system that multiplies a transmission signal by a transmission antenna weight that is different for each stream.
In the closed-loop MIMO wireless transmission system (Closed-Loop MIMO) of the present embodiment, a case of a configuration of a 2-transmission layer (number of ranks 2) conforming to the LTE communication standard will be exemplified. However, the present invention is not limited to this configuration.

  In FIG. 1, a user device 10 is a wireless communication device that can be used when a user uses various communication services, and is referred to as a “communication terminal” or a “terminal” or can be moved. Sometimes called a “station”, sometimes called a “radio”. The user device 10 may be a mobile communication terminal such as a mobile phone. As shown in FIG. 1, the user apparatus 10 includes a plurality of antennas 100, a downlink channel estimation unit 101, a downlink control signal demodulation unit 102, a data signal demultiplexing / combining unit 103, and a serial / parallel conversion unit (S / P) 104, a control information (RI / PMI / CQI) generation unit 105, and an uplink transmission unit 106.

  In the example of FIG. 1, the user apparatus 10 includes a plurality of antennas 100, but the number of antennas 100 included in the user apparatus 10 is not limited to a specific number. For example, the user apparatus 10 may be provided with a single antenna 100 or may be provided with a plurality of antennas 100 such as two or four. Further, when the user apparatus 10 includes a plurality of antennas 100, the user apparatus 10 may be capable of switching the number of antennas used during actual MIMO communication.

  Also, in the downlink channel estimation unit 101 of the user apparatus 10, the radio channel response between each antenna 200 of the base station apparatus 20 to each antenna of the user apparatus 10 is estimated and the MIMO channel response is acquired. The multiplexer 208 of the station 20 multiplexes a reference signal RS, which is a predetermined pilot signal, which is not shown in the figure. Here, since the reference signal RS is a signal specific to a cell, it is also called a cell-specific reference signal (CSRS).

  The downlink channel estimation unit 101 first divides the received signal from each antenna 100 into received signals of a reference signal RS part, a data signal part, and a downlink control signal part. Next, the MIMO channel response is estimated based on the received signal of the reference signal RS portion and the transmission sequence of the predetermined reference signal RS. Then, the channel estimation value, which is the estimation result of the MIMO channel response, is output to the data signal demultiplexing unit 103 and the downlink control signal demodulating unit together with the received signals of the data signal portion and the downlink control signal portion. Further, the channel estimation value is output to control information (RI / PMI / CQI) generation section 105.

  The downlink control signal demodulator 102 demodulates the control signal from the received signal received from the downlink channel estimator 101, and MCS (Modulation and Coding Scheme), which is transmission scheme information necessary for demodulating and decoding user data. ), Rank (Rank), and T-PMI (Transmit-Precoding Matrix Indicator) control information, and outputs it to the data signal demultiplexing / combining unit 103.

  The data signal demultiplexing / combining unit 103 demultiplexes and / or combines the received signals of the user data received from the downlink channel estimation unit 101 based on the control information received from the downlink control signal demodulating unit 102, and a predetermined number of codes It outputs to the serial / parallel conversion part (S / P) 104 as data consisting of words.

  The serial-to-parallel converter (S / P) 104 converts the data consisting of a predetermined number of codewords received from the data signal separation / combination unit 103 according to the number of downlink ranks into received data (user data ).

  Control information (RI / PMI / CQI) generation section 105 determines a rank for maximizing the data rate based on the channel estimation value received from downlink channel estimation section 101, and determines this rank as rank information (RI: Rank). (Indicator) and output. Also, the control information (RI / PMI / CQI) generation unit 105 determines a precoding matrix suitable for downlink data transmission based on the channel estimation value, and a PMI (Precoding Matrix Indicator) indicating this precoding matrix ) Is selected from the candidate data table (codebook) and output. Further, control information (RI / PMI / CQI) generation section 105 measures and outputs CQI (Channel Quality Indicator) as channel quality information based on the channel estimation value. The rank information RI, PMI, and CQI output from the control information (RI / PMI / CQI) generation unit 105 are respectively output to the uplink transmission unit 106 as control information, and the uplink control channel (PUCCH or PUSCH) is selected. Via the antenna 100 to the radio base station 20.

In particular, the downlink channel estimation unit 101 and the control information (RI / PMI / CQI) generation unit 105 also function as the following means (1) to (4).
(1) Based on the reception result of the reference signal RS, which is a known pilot signal transmitted and received between the user apparatus 10 and the radio base station 20, between the MIMO channels between the user apparatus 10 and the radio base station 20 Calculating means for calculating a plurality of eigenvalues of a correlation matrix of a MIMO channel matrix indicating the correlation of
(2) Interference noise level estimation means for estimating the interference noise level in the MIMO channel based on the reception result of the reference signal RS which is the known pilot signal.
(3) Threshold setting means for setting a threshold based on the estimation result of the interference noise level.
(4) Rank information generating means for generating rank information indicating the number of transmission layers used for data transmission / reception in a MIMO channel based on a comparison result between the calculated plurality of eigenvalues and the threshold.

  The uplink transmission unit 106 also functions as rank information transmission means for transmitting the rank information RI generated by the control information (RI / PMI / CQI) generation unit 105 to the radio base station 20.

The user apparatus 10 having the configuration of FIG. 1 estimates a MIMO channel response based on a reception result of a reference signal RS that is a known downlink pilot signal, obtains a channel estimation value, and obtains optimum rank information from the channel estimation value. The RI is determined, and the value of the rank information RI is fed back to the radio base station 20 together with the optimum PMI / CQI.
As in the specification of 3GPP LTE (Long Term Evolution), when the transmission timing of rank information RI overlaps with the transmission timing of PMI or CQI as other control information, transmission of rank information RI is given priority. The

  In FIG. 1, the radio base station 20 is a radio communication device that relays radio communication between the communication network side and the user terminal device 10, and is called a “base station device” or simply called a “base station”. Sometimes it is. Also, the radio base station 20 may be called “eNodeB (evolved Node B)” in the 3GPP and LTE specifications.

  As illustrated in FIG. 1, the radio base station 20 includes a plurality of antennas 200, an uplink reception unit 201, a downlink scheduler 202, a precoding weight generation unit 203, and a downlink control signal generation unit 204. A parallel conversion / modulation unit 205, a multiplier 206, an addition processing unit (Σ) 207, and a multiplexer 208 are provided.

  In the example of FIG. 1, the radio base station 20 includes a plurality of antennas 200, but the number of antennas 200 included in the radio base station 20 is not limited to a specific number. For example, the radio base station 20 may include a single antenna 200 or may include a plurality of antennas 200 such as two or four. Further, when the radio base station 20 includes a plurality of antennas 200, the radio base station 20 may be capable of switching the number of antennas used in actual MIMO communication.

  The uplink receiving unit 201 receives control information (RI, CQI, PMI) from the user apparatus 10 via the uplink control channel (PUCCH), and sends it to the downlink scheduler 202.

  The downlink scheduler 202 determines various control parameters used in the downlink with the user apparatus 10 based on the control information (RI, CQI, PMI) received from the uplink receiving unit 201. For example, the downlink scheduler 202 determines a rank number (Rank) indicating the number of spatially multiplexed transmission layers, a T-PMI that specifies a transmission precoding matrix, and an MCS that specifies a modulation and coding scheme. Then, the downlink scheduler 202 sends the determined MCS and Rank signals to the serial-to-parallel conversion / modulation unit 205, and sends the Rank and T-PMI signals to the precoding weight generation unit 203, and the MCS, Rank, and The T-PMI signal is sent to the downlink control signal generator 204.

  Based on the Rank and T-PMI signals received from the downlink scheduler 202, the precoding weight generation unit 203 transmits each of the plurality of antennas 200 based on the uplink reception quality in the resource block allocated to the user apparatus 10. Precoding weights for controlling the phase and / or amplitude of the signal are generated and sent to the multiplier 206.

  The downlink control signal generation unit 204 generates a reference signal RS and a control signal used in the downlink based on the MCS, Rank, and T-PMI signals received from the downlink scheduler 202, and sends them to the multiplexer 208.

  The serial-parallel conversion / modulation unit 205 distributes user data to be transmitted to the number of transmission layers based on the rank number (Rank) received from the downlink scheduler 202. The multiplier 206 includes three systems of multipliers 206a, 206b, and 206c corresponding to the three antennas 200. When user data is input, data received from the downlink scheduler 202 by the serial-to-parallel converter / modulator 205 is multiplied by transmission data by multipliers 206a, 206b, and 206c, and the phase and amplitude are respectively controlled. By (shifting), a transmission signal is generated for each of the plurality of antennas 200. Then, the transmission signals generated by being distributed to a plurality of transmission layers (two layers in the example of FIG. 1) are added by the adder (Σ) 207 for each transmission layer, and then the reference signal RS and the multiplexer 208 Control signals are further multiplexed and transmitted from each of the three antennas 200.

In the MIMO radio transmission system having the configuration shown in FIG. 1, the rank number Rank is determined by the radio base station 20 based on the rank information RI fed back from the user apparatus 10 as described above. For example, the rank number Rank = 1 when the rank information RI = 1, and the rank number Rank = 2 is normally selected when the rank information RI = 2. When the rank number Rank = 1, single transmission beam forming is performed, and when the rank number Rank ≧ 2, multi-beam transmission spatial multiplexing is performed.
As in the 3GPP specifications, since the radio base station 20 side has the final decision right of the rank number Rank, when determining the rank number Rank on the radio base station 20 side, the rank information RI of the user apparatus 10 is determined. It is not always necessary to follow the value of.

FIG. 2 is a functional block diagram illustrating an example of a schematic configuration of a radio base station and a user apparatus in the downlink of an open-loop MIMO radio transmission system (Open-Loop MIMO) according to another embodiment to which the present invention is applicable. It is.
The MIMO radio transmission system in FIG. 2 is an open-loop MIMO radio transmission system that feeds back rank information RI and CQI from the user apparatus 10 to the radio base station 20 but does not feed back PMI. In addition, the same code | symbol is attached | subjected about the structure similar to the said FIG. 1, and detailed description is abbreviate | omitted.

  In FIG. 2, the control information (RI / CQI) generation unit 115 of the user apparatus 10 determines a rank that maximizes the data rate based on the channel estimation value received from the downlink channel estimation unit 101, and determines this rank. Generate and output as rank information RI. Control information (RI / CQI) generation section 115 measures and outputs CQI as channel quality information based on the channel estimation value received from downlink channel estimation section 101. The rank information RI and CQI output from the control information (RI / CQI) generation unit 115 are output as control information to the uplink transmission unit 106 and transmitted to the radio base station 20 via the antenna 100. Unlike the configuration of FIG. 1 described above, PMI determination and transmission are not performed.

In this way, the user apparatus 10 having the configuration of FIG. 2 estimates the MIMO channel response based on the reception result of the reference signal RS, which is a known downlink pilot signal, and obtains a channel estimate, and from the channel estimate The rank information RI is determined, and the value of the rank information RI is transmitted to the radio base station 20 via the uplink control channel (PUCCH or PUSCH) together with the optimum CQI and fed back.
As in the 3GPP specification, when the transmission timing of rank information RI overlaps with the transmission timing of CQI, which is other control information, transmission of rank information RI is given priority.

In FIG. 2, the downlink scheduler 202 of the radio base station 20 uses various control parameters used in the downlink with the user apparatus 10 based on the control information (RI, CQI) received from the uplink receiving unit 201. To decide. For example, the downlink scheduler 202 determines a rank number (Rank) indicating the number of spatially multiplexed transmission layers and an MCS that specifies a modulation and coding scheme. Then, the downlink scheduler 202 sends the determined MCS and Rank signals to the serial-parallel conversion / modulation unit 205, sends the Rank signal to the precoding weight generation unit 203, and transmits the MCS and Rank signals to the downlink. It transmits to the control signal generation unit 204.
Note that the radio base station 20 having the configuration of FIG. 2 does not receive PMI from the user apparatus 10 and generate T-PMI based on the PMI reception result. The precoding weight generation unit 203 and the downlink control signal generation unit 204 use a precoding scheme that is predefined in the specification without using the PMI from the user apparatus 10.

In the MIMO radio transmission system having the configuration shown in FIG. 2, the rank number Rank is determined by the radio base station 20 based on the rank information RI fed back from the user apparatus 10 as described above. For example, the rank number Rank = 1 when the information RI = 1, and the rank number Rank = 2 is normally selected when the rank information RI = 2. When the rank number Rank = 1, transmission diversity using SFBC (spatial frequency block coding) is used, and when the rank number Rank ≧ 2, spatial multiplexing using CDD (code division duplex) is used.
In the MIMO radio transmission system having the configuration shown in FIG. 2 as well, the final decision on the rank number Rank is held by the radio base station 20 as in the 3GPP specifications, so that the rank number Rank is set on the radio base station 20 side. When determining, it is not necessary to follow the value of the rank information RI of the user device 10.

  In the MIMO radio transmission system of FIG. 1 and FIG. 2 described above, the determination of the optimum number of transmission layers for the downlink from the radio base station 20 to the user apparatus 10 has been described. The present invention can also be applied to the case of uplink for transmitting data to.

  FIG. 3 is a functional block diagram showing an example of a schematic configuration of a radio base station and user equipment in an uplink of a closed-loop MIMO radio transmission system according to still another embodiment to which the present invention is applicable. In the closed-loop type MIMO wireless transmission system of the present embodiment, a case of a configuration of a 2-transmission layer (rank number is 2) conforming to the LTE-Advanced communication standard is illustrated, but the present invention has this configuration. It is not limited. Further, detailed description of the same configuration as in FIG. 1 is omitted.

  As shown in FIG. 3, the user apparatus 30 includes a plurality of antennas 300, a downlink reception unit 301, a precoding weight generation unit 302, a serial / parallel conversion / modulation unit 303, a multiplier 304, and an adder ( Σ) 305, a multiplexer 306, and an uplink reference signal generation unit 307.

  In the example of FIG. 3, the user apparatus 30 includes a plurality of antennas 300, but the number of antennas 300 included in the user apparatus 30 is not limited to a specific number. For example, the user apparatus 30 may be provided with one antenna 300 or may be provided with a plurality of antennas 300 such as two or four. Further, when the user apparatus 30 includes a plurality of antennas 300, the user apparatus 30 may be capable of switching the number of antennas used during actual MIMO communication.

  In the user apparatus 30, the reference signal RS generated by the uplink reference signal generation unit 307 is multiplexed with another control signal by the multiplexer 306 and transmitted from the plurality of antennas 300.

  Also, the user apparatus 30 separates the control information (RI, MCS, PMI) included in the downlink control channel received from the radio base station 40 by the downlink receiving unit 301, and the PMI is sent to the precoding weight generating unit 302. The RI and the MCS are output to the serial / parallel conversion / modulation unit 303. Thereby, the user apparatus 30 transmits user data on the uplink data channel according to the RI, MCS, and PMI included in the received downlink control channel.

  As shown in FIG. 3, the radio base station 40 includes a plurality of (in this example, three) antennas 400, an uplink channel estimation unit 401, a data signal separation / combination unit 402, and a serial / parallel conversion unit (S / P) 403, an uplink scheduler 404, and a downlink transmission unit 405.

  In the radio base station 40, signals received by the plurality of antennas 400 are sent to the uplink channel estimation unit 401. Uplink channel estimation section 401 corrects the distortion of the signal from each antenna 400 and outputs the received signal after the distortion correction to data signal demultiplexing and combining section 402. Further, the uplink channel estimation unit 401 estimates a MIMO channel response based on the reference signal RS as a predetermined pilot signal received from the user apparatus 30, and sets a channel estimation value that is an estimation result of the MIMO channel response to the uplink. The data is output to the scheduler 404.

  The uplink scheduler 404 determines various control parameters used in the uplink with the user apparatus 10 based on the channel estimation value received from the uplink channel estimation unit 401. For example, the uplink scheduler 404 generates and outputs rank information RI indicating the number of spatially multiplexed transmission layers that maximizes the data rate in the uplink. Also, the uplink scheduler 404 determines a precoding matrix suitable for uplink data transmission / reception, and selects and outputs a PMI indicating the precoding matrix from the codebook. Also, the uplink scheduler 404 determines and outputs an MCS that specifies a modulation and coding scheme. Then, the uplink scheduler 404 sends the rank information RI to the serial / parallel conversion unit (S / P) 403, and transmits the RI information, MCS, and PMI to the data signal separation / combination unit 402 and the downlink transmission unit 405. The downlink transmission unit 405 transmits the rank information RI received from the uplink scheduler 404 to the user apparatus 30 via the downlink control channel (PDCCH) and feeds it back.

  In LTE-Advanced, since the radio base station 40 has the right to determine the transmission method of the user apparatus 30 for both downlink and uplink, the rank information RI calculated by the uplink scheduler 404 of the radio base station 40 remains as it is. It becomes the rank number Rank of the uplink.

  In the uplink configuration of FIG. 3, the uplink channel estimation unit 401 and the uplink scheduler 404 also function as the above-described calculation means, interference noise level estimation means, threshold setting means, and rank information generation means. The downlink transmission unit 405 also functions as rank information transmission means for transmitting the rank information RI generated by the uplink scheduler 404 to the user apparatus 30.

  Next, generation of rank information (RI) in the MIMO wireless transmission system of FIGS. The generation of the rank information RI in the user apparatuses 10 and 30 and the radio base station 40 in the present embodiment can be explained by a model using the MIMO channel matrix shown below. In the following description, data communication between the user apparatus and the radio base station is performed using a plurality of subcarriers. The number of subcarriers is Nsc, and k indicates a subcarrier number.

FIG. 4 is a schematic diagram showing each element of the MIMO channel matrix obtained by equivalently converting the transmission path between the radio base station and the user apparatus. Also, the MIMO channel matrix shown in FIG. 4 is expressed as the following equation.

Further, the matrix H (k) of the above equation 1 is obtained by using a general SVD (Singular Value Decomposition) technique, and the three matrices U (k), Σ (k), V ( k) can be decomposed into products.

However, U (k) is called a left singular vector matrix, Σ (k) is called a singular value matrix, and V (k) is called a right singular vector matrix, which are expressed by the following equations 3 to 5, respectively.

  Further, the diagonal elements of the matrix Σ (k) in the equation (4) indicate singular values of the matrix H (k) in the equation (2).

FIG. 5 is a schematic diagram showing an equivalent circuit of the MIMO channel matrix in the equivalent conversion of the MIMO channel matrix. Here, in the equivalent circuit of the MIMO channel matrix of FIG. 5, the number of equivalent transmission lines that can actually transmit signals (hereinafter referred to as “the number of equivalent transmission lines”) is the maximum M = min (N _r , N _t ).

In addition, values λ ₁ (k) to λ _M (k) obtained by squaring each singular value of the matrix H (k) are the eigenvalues of H (k) H ^H (k) or H (k) ^H H (k). They coincide and all become real numbers of 0 or more as shown in the following equation (7).

The number 2 in the formula of the left singular vectors matrix U (k) and the right singular vectors matrices V (k) are respectively H ^{(k) H} matrix composed of eigenvectors of H (k) and ^{H H} (k) ^H This is a matrix composed of eigenvectors of (k), and each has the property of a unitary matrix as shown in the following equations (8) and (9). Here, I represents the unit matrix, and the superscript H represents the complex conjugate transpose of the matrix or vector.

FIG. 6 is a schematic diagram showing the notation of the channel matrix in the SVD-MIMO transmission model. Each determinant in FIG. 6 is expressed by the following equation.

In the above equation (10), y (k) represents a received signal when V (k) is used as precoding on the transmission side and U ^H (k) is used as spatial filtering on the reception side. Since the Σ term included in the expression of y (k) is a diagonal matrix of singular values, there is no intersubstream (transmission layer). This is because interference between substreams (transmission layers) can be removed by using V (k) as precoding on the transmission side and U ^H (k) as spatial filtering on the reception side. It shows that multiplex transmission can be realized.

FIG. 7 is a schematic diagram showing the notation of the channel matrix in the SVD-MIMO transmission equivalent model.
In FIG. 7, if a complete MIMO channel matrix or optimum transmission weight vector V (k) can be acquired on the transmission side, it can be decomposed into M independent SISO (Single Input Single Output) channels. The propagation path gain of the _mth SISO channel is represented by λ _m (k).

Here, when the average interference noise level is σ ² and the average signal strength is P _m ^(s) λ _m (k), the channel capacity C (k) is expressed by the following equation.

Note that the channel capacity C (k) represented by the above equation 11 is a so-called Shannon capacity and corresponds to the limit of the theoretical data capacity (channel capacity) that can be transmitted on the communication transmission path. In a method called “water injection theorem” in the conventional SVD-MIMO transmission scheme, the Shannon capacity is maximized when the total transmission power P _total transmitted through the MIMO channel is constant as shown in the following equation (12). Thus, optimal power distribution for each transmission layer is performed. Here, α in the formula 12 is a coefficient for satisfying the following formula 13.

  However, as shown below, the water injection theorem in the SVD-MIMO transmission method is not an optimal method when considering a realistic modulation method and error correction coding method. In the water injection theorem in the SVD-MIMO transmission scheme, the channel capacity is maximized by not performing transmission power distribution for subchannels whose signal reception level is close to the interference noise level. Also, the SVD-MIMO transmission scheme can be realized only when complete channel information is obtained on the transmission side or when an ideal transmission weight vector V (k) is obtained on the transmission side.

  In an actual system, there is a control delay, and FDD (Frequency Division Duplex) has a restriction on the amount of feedback information. For example, in LTE, as information corresponding to the average received SINR, discrete CQI, PMI, or MCS expressed in about several bits is fed back to the transmission side. In LTE / LTE-Advanced, rank adaptation using rank information RI is performed for the purpose of not allocating transmission power to sub-channels with poor quality in order to obtain performance that approaches the Shannon limit efficiently while the amount of channel information feedback is limited. It can be thought that it was introduced.

Also, in OFDM (Orthogonal Frequency Division Multiple) that is error correction coded in the frequency direction, controlling the number of transmission layers in units of subcarriers increases the number of transport block size candidates. Not realistic. Therefore, in LTE / LTE-Advanced, the number of transmission layers (rank) is controlled in units of error correction coding. For this reason, it is necessary to control the number of transmission layers based on the average characteristic between subcarriers. In particular, in LTE, since the precoding matrix applicable on the transmission side is discrete, it is not optimal to allocate transmission power by the water injection theorem. Further, in MIMO precoded based on incomplete channel information, transmission performance depends on a reception algorithm.
For the above reason, it is difficult to theoretically determine the optimum rank information RI in a MIMO wireless transmission system using OFDM, and it must be a trial and error determination method.

Therefore, in the MIMO wireless transmission system according to the present embodiment shown in FIGS. 1 to 3, the optimum rank information RI is generated while paying attention to the following points (1) to (3).
(1) Since the lower rank transmission is desirable as the received SINR becomes lower or the fading correlation becomes higher, rank information adapted to it can be generated.
(2) The actual throughput is different from the theoretical capacity limit (Shannon capacity).
(3) Since the optimum number of transmission layers is considered to differ depending on the reception algorithm, it can be tuned by simple parameter adjustment.

In consideration of the above points (1) to (3), the generation of the optimum rank information RI in the present embodiment is performed as follows, for example.
First, the average of the eigenvalues of the correlation matrix H (k) H ^H (k) or H ^H (k) H (k) of the MIMO channel (hereinafter referred to as “average eigenvalue” as appropriate) is expressed by the following equation. Ask. Incidentally, the N _SC in the formula is the total number of subcarriers.

  As the MIMO channel matrix, the channel estimation result of the MIMO channel response estimated based on the received signal of the reference signal RS is used. Here, the method of averaging the eigenvalues between subcarriers may be a method performed on all subcarriers, or a method performed on some subcarriers such as a subcarrier on which the reference signal RS is multiplexed. .

Next, the average interference noise level σ ² is estimated based on the received signal of the reference signal RS. Here, the method of averaging the interference noise level may be a method performed on all subcarriers, or a method performed on some subcarriers such as a subcarrier on which the reference signal RS is multiplexed.

As a method of estimating the average interference noise level σ ² , for example, a method of obtaining a primary channel estimated value from the received signal of the reference signal RS and obtaining an interference noise power estimated value from the primary channel estimated value can be used. (For example, refer nonpatent literature 5) However, it is not limited to this method.

Next, based on the estimated average interference noise level σ ² , a threshold value β that is a parameter for generating RI is determined. Specifically, as shown in the following equation 15, the estimated average interference noise level σ ² is offset by a predetermined offset amount Δ [dB], and a value normalized by the total transmission power P _total is expressed as follows: The threshold value β is determined.

  Note that the offset amount Δ used when determining the threshold value β is optimal by computer simulation, experiment, etc. in consideration of channel estimation and signal separation algorithm in an actual MIMO transmission method (Open Loop-MIMO, Closed-Loop MIMO). Determine the value.

  Next, the number of average eigenvalues exceeding the threshold β (effective rank of the MIMO channel) is calculated, and rank information RI is generated based on the calculation result. Here, when the calculated effective rank is 0, rank information RI = 1 is set. In other cases, the effective rank value is set to the rank information RI value.

FIG. 8 is an explanatory diagram for setting the rank information RI based on the average eigenvalue and the threshold value β when the number of equivalent transmission lines M in the SVD-MIMO transmission equivalent model is an arbitrary number. The rank information RI is set as shown in FIG.

  For example, when the number of average eigenvalues exceeding the threshold β is 0 or when the maximum average eigenvalue is equal to the threshold β, the rank information RI = 1 is set. When the number of average eigenvalues exceeding the threshold β is m, rank information RI = m is set. When all the M average eigenvalues exceed the threshold value β or when the minimum average eigenvalue is equal to the threshold value β, the rank information RI = M is set. That is, the rank information RI can be set by a simple comparison calculation process in which M average eigenvalues are compared with the threshold value β.

FIG. 9 is an explanatory diagram for setting the rank information RI based on the average eigenvalue and the threshold value β when the number of equivalent transmission lines M is two.
In FIG. 9, when neither of the _two average eigenvalues λ ₁ and λ ₂ exceeds the threshold value β, that is, when the minimum average eigenvalue λ ₂ is equal to or less than the threshold value β, the rank information RI = 1 is set. The maximum average eigenvalue lambda ₁ exceeds the threshold value beta, and the minimum average eigenvalue lambda ₂ even when less than the threshold value beta, sets the rank information RI = 1. When both of the two average eigenvalues λ ₁ and λ ₂ exceed the threshold value β, that is, when the minimum average eigenvalue λ ₂ exceeds the threshold value β, the rank information RI = 2 is set. That is, in the example of FIG. 9, the rank information RI can be set by a simple comparison calculation process of comparing the minimum average eigenvalue λ2 and the threshold value β.

As described above, according to the present embodiment, data transmission / reception by a plurality of different transmission layers using a plurality of antennas is performed between a user apparatus 10 (30) as a plurality of radio communication apparatuses and a radio base station 20 (40). In the wireless transmission system to perform, based on the reception result of the reference signal RS as a known pilot signal transmitted / received between the user apparatus 10 (30) and the wireless base station 20 (40), the user apparatus and the wireless base station A plurality of eigenvalues λ of the correlation matrix of the MIMO channel matrix indicating the wireless transmission characteristics of the MIMO channel between the two are calculated. Further, the interference noise level σ ² in the MIMO channel is estimated based on the reception result of the known reference signal RS, and the threshold value β is set based on the estimation result of the interference noise level σ ² . Then, rank information RI indicating the number of transmission layers used for data transmission / reception in the MIMO channel is generated based on the comparison result between the plurality of eigenvalues λ and the threshold value β. The calculated number of eigenvalues λ is the maximum number of virtual SISO (Single Input Single Output) channels obtained by decomposing MIMO channels so as to be independent and in parallel, that is, data can be transmitted independently of each other. This corresponds to the maximum number M of transmission layers. Each of the plurality of eigenvalues λ corresponds to the transmission gain of the transmission path formed in the SISO channel, that is, the transmission layer. Here, if an eigenvalue λ having a value larger than a predetermined threshold β is selected and a transmission layer corresponding to the selected eigenvalue λ is used, data is transmitted only by a transmission layer having a predetermined transmission gain. Therefore, the data capacity that can be transmitted and received by the MIMO channel can be brought close to the theoretical capacity limit (Shannon capacity). Therefore, by generating rank information indicating the number of transmission layers used for data transmission / reception in the MIMO channel based on a comparison result between a plurality of eigenvalues λ and a predetermined threshold β, the data capacity that can be transmitted / received in the MIMO channel It is possible to generate the optimum rank information RI that can approach the theoretical capacity limit (Shannon capacity).
In addition, in the present embodiment, the interference noise level σ ² estimated based on the reception result of the known reference signal RS is different from that in the surrounding cell particularly in the case of a cellular environment where a plurality of base station apparatuses are expanded. This is increased or decreased depending on the user's communication status, etc., and reflects the state of the radio transmission path in the MIMO channel. In this way, the interference noise level σ ² reflecting the state of the radio transmission path in the MIMO channel is estimated, and a threshold value β to be compared with the plurality of eigenvalues λ is set based on the estimation result of the interference noise level σ ^2. Yes. This threshold value β reflects the state of the radio transmission path in the MIMO channel, and can be arbitrarily adjusted by simple processing such as changing according to the type of reception algorithm. Then, the threshold value β thus set is compared with a plurality of eigenvalues λ, and rank information RI indicating the number of transmission layers used for data transmission / reception in the MIMO channel is generated based on the comparison result, thereby receiving SINR and fading. In addition to adapting to changes in the state of the wireless transmission path such as correlation, rank information can be generated by absorbing differences in wireless transmission characteristics (throughput characteristics) depending on the type of reception algorithm.
Further, according to the present embodiment, when the maximum number of transmission layers M of the MIMO channel is 2, the minimum value is obtained for the plurality of eigenvalues λ, and is optimal when the minimum value is greater than or equal to the threshold β or larger than the threshold β. The rank information RI (number of transmission layers) is set to 2. Thus, when the maximum number of transmission layers M is 2, if the minimum value of the plurality of eigenvalues λ is greater than or equal to the threshold value β or greater than the threshold value β, the other eigenvalues are also greater than or equal to the threshold value β or greater than the threshold value β. What is necessary is just to compare with the threshold value (beta). The rank information RI is set to 2 when the minimum value of the eigenvalue is equal to or larger than the threshold value β or larger than the threshold value β, and the rank information RI is set to 1 otherwise. Therefore, it becomes easy to calculate and set the rank information RI.
Further, according to the present embodiment, the threshold value β is obtained by offsetting the interference noise level σ ² by a preset offset amount Δ and normalizing with the total transmission power of the reference signal RS. As a result, the simple process of offsetting the interference noise level σ ² by a predetermined offset amount Δ only allows adjustment of the threshold β taking into account the difference in radio transmission characteristics depending on the type of the reception algorithm. In addition, the influence of the transmission power on the rank information RI generated based on the threshold value β can be reduced.
Further, according to the present embodiment, transmission / reception between the user apparatus 10 (30) and the radio base station 20 (40) is performed using a plurality of subcarriers, and transmission / reception is performed between the user apparatus and the radio base station. Based on the reception result of the known reference signal RS by each of the plurality of subcarriers, an average value between the plurality of subcarriers is calculated for each of the plurality of eigenvalues λ of the MIMO channel matrix. Further, based on the reception result of the known reference signal RS by each of the plurality of subcarriers, the interference noise level σ ² in the MIMO channel is estimated, and based on the comparison result between the average value of the plurality of eigenvalues λ and the threshold value β. Then, rank information RI of the MIMO channel is generated. This makes it possible to generate optimal rank information RI even in data transmission / reception using a plurality of subcarriers.
Further, according to the present embodiment, the average value of the eigenvalues λ is an average obtained by weighting each subcarrier. Thereby, the accuracy of the average value of the eigenvalues λ used for generating the rank information RI can be improved.

In each of the above embodiments, the eigenvalue (λ) of the correlation matrix of the MIMO channel matrix is used to generate the rank information RI, but the singular value ((λ) ^1/2 ) of the MIMO channel matrix may be used. Good. In this case, for example, values obtained by squaring a plurality of singular values of the MIMO channel matrix based on the reception result of the reference signal RS by each of the plurality of subcarriers transmitted and received between the plurality of user apparatuses 10 (30). The average value among the plurality of subcarriers is calculated for the sub-carrier, and rank information RI of the MIMO channel is generated based on the comparison result between the mean square value of the plurality of singular values and the threshold value β.

DESCRIPTION OF SYMBOLS 10, 30 User apparatus 20, 40 Radio base station 101 Downlink channel estimation part 102 Downlink control signal demodulation part 103 Data signal demultiplexing / combination part 104 Serial / parallel conversion part 105 Control information (RI / PMI / CQI) generation part 106 Uplink Transmission unit 201 Uplink reception unit 202 Downlink scheduler 203 Precoding weight generation unit 204 Downlink control signal generation unit 205 Serial / parallel conversion / modulation unit 206 Multiplier 208 Multiplexer 301 Downlink reception unit 302 Precoding weight generation unit 303 Serial parallel Conversion / Modulation Unit 304 Multiplier 307 Uplink Reference Signal Generation Unit 401 Uplink Channel Estimation Unit 404 Uplink Scheduler 405 Downlink Transmitter

JP 2010-148004 A

3GPP TS36.211 V10.1.0, "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 10)," March 2011. 3GPP TS36.212 V10.1.0, "Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding (Release 10)," March 2011. 3GPP TS36.213 V10.1.0, "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 10)," March 2011. H. Taoka, S. Nagata, K Takeda, Y. Kakishima, X. She, and K. Kusume, "MIMO and CoMP in LTE-Advanced," NTT DoCoMo Technical Journal (English Edition), vol.12, no.2 , pp.20-28, Sept. 2010. S. Boumard, "Novel noise variance and SNR estimation algorithm for wireless MIMO OFDM systems," Proceedings of IEEE Global Telecommunications Conference 2003, vol.3, pp.1330-1334, San Francisco, USA, Dec. 2003.

Claims (7)

A wireless transmission system that transmits and receives data by a plurality of different transmission layers between a plurality of wireless communication devices,
A plurality of singular values of a MIMO channel matrix indicating a transmission characteristic of a MIMO channel between the plurality of wireless communication devices based on reception results of known pilot signals transmitted / received between the plurality of wireless communication devices or the MIMO Calculating means for calculating a plurality of eigenvalues of the correlation matrix of the channel matrix;
Interference noise level estimation means for estimating an interference noise level in the MIMO channel based on the reception result of the known pilot signal;
A value obtained by offsetting the previously only determined offset the interference noise level estimation result based on the received algorithm used for communication between the plurality of wireless communication devices, and a threshold setting means for setting a threshold value,
Rank information generating means for generating rank information indicating the number of transmission layers used for data transmission / reception in the MIMO channel based on a comparison result between the plurality of singular values or the plurality of eigenvalues and the threshold;
A wireless transmission system comprising: The wireless transmission system of claim 1,
When the maximum number of transmission layers of the MIMO channel is 2, the rank information generation unit obtains a minimum value for a value obtained by squaring the plurality of singular values or the plurality of eigenvalues, and the minimum value is equal to or greater than the threshold value or the threshold value wireless transmission system, characterized in that the 2 number transmit layer used for data transmission and reception in the large case, the MIMO channel than. The wireless transmission system according to claim 1 or 2,
The threshold value, the wireless transmission system, characterized in that said at the interference noise level estimation result obtained by normalizing the total transmission power of the previous SL pilot signal values offset by said offset amount. The wireless transmission system according to claim 1, 2 or 3,
Transmission / reception between the plurality of wireless communication devices is performed using a plurality of subcarriers,
The calculation means is a value obtained by squaring a plurality of singular values of the MIMO channel matrix based on reception results of known pilot signals by each of the plurality of subcarriers transmitted and received between the plurality of wireless communication devices, or For each of a plurality of eigenvalues of the correlation matrix of the MIMO channel matrix, an average value between the plurality of subcarriers is calculated,
The interference noise level estimation means estimates an interference noise level in the MIMO channel based on a reception result of a known pilot signal by each of the plurality of subcarriers,
The rank information generating means generates rank information of the MIMO channel based on a comparison result between a mean square value of the plurality of singular values or an average value of the plurality of eigenvalues and the threshold value. Wireless transmission system. The wireless transmission system according to claim 1, 2, 3 or 4 ,
The plurality of wireless communication devices are configured using a data transmission-side wireless communication device that transmits data and a data reception-side wireless communication device that receives the data,
The wireless communication device on the data receiving side includes the calculating means, the interference noise level estimating means, the threshold setting means, and the rank information generating means, and the rank information generated by the rank information generating means is It further comprises rank information transmission means for transmitting to the wireless communication device on the data transmission side,
The data transmission side wireless communication apparatus includes rank information reception means for receiving the rank information from the data reception side wireless communication apparatus, and a number indicated by the rank information based on the rank information by the rank information reception means. And a data transmission means for transmitting data to the data reception-side wireless communication apparatus using a transmission layer of the wireless transmission system. A wireless communication device on a data receiving side that receives the data in a wireless transmission system that transmits and receives data by a plurality of different transmission layers between a plurality of wireless communication devices,
A plurality of singular values of a MIMO channel matrix indicating a transmission characteristic of a MIMO channel between the plurality of wireless communication devices based on reception results of known pilot signals transmitted / received between the plurality of wireless communication devices or the MIMO Calculating means for calculating a plurality of eigenvalues of the correlation matrix of the channel matrix;
Interference noise level estimation means for estimating an interference noise level in the MIMO channel based on the reception result of the known pilot signal;
A value obtained by offsetting the previously only determined offset the interference noise level estimation result based on the received algorithm used for communication between the plurality of wireless communication devices, and a threshold setting means for setting a threshold value,
Rank information generating means for generating rank information indicating the number of transmission layers used for data transmission / reception in the MIMO channel based on a comparison result between the plurality of singular values or the plurality of eigenvalues and the threshold;
Rank information transmission means for transmitting the rank information generated by the rank information generation means to a wireless communication device on the data transmission side for transmitting the data;
A wireless communication apparatus comprising: A wireless transmission method for transmitting and receiving data by a plurality of different transmission layers between a plurality of wireless communication devices,
A plurality of singular values of a MIMO channel matrix indicating a transmission characteristic of a MIMO channel between the plurality of wireless communication devices based on reception results of known pilot signals transmitted / received between the plurality of wireless communication devices or the MIMO Calculating a plurality of eigenvalues of the correlation matrix of the channel matrix;
Estimating an interference noise level in the MIMO channel based on a reception result of the known pilot signal;
A step of a value obtained by offsetting the previously only determined offset the interference noise level estimation result based on the received algorithm used for communication between the plurality of wireless communication devices, to set a threshold value,
Generating rank information indicating the number of transmission layers used for data transmission / reception in the MIMO channel based on a comparison result between the plurality of singular values or the plurality of eigenvalues and the threshold;
Transmitting and receiving data between the plurality of wireless communication devices by the number of transmission layers indicated by the rank information;
A wireless transmission method comprising:

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