JPWO2016121257A1 - Wireless communication apparatus and signal processing control method - Google Patents

Abstract

A wireless communication device that communicates with a subordinate radio communication device, estimates the channel quality of a channel used for feedback of a signal from the subordinate radio communication device, and considers the estimated channel quality, Whether the control unit performs scheduling for allocating radio resources to subordinate radio communication devices, and the control unit sets the subordinate radio communication device that has fed back a signal based on the estimated channel quality as a target of spatial multiplexing communication When determining whether or not to make a spatial multiplexing communication target, scheduling is performed so as to perform spatial multiplexing communication with a subordinate radio communication apparatus.

Description

  The present invention relates to a radio communication apparatus, and more particularly, to a radio communication apparatus constituting a radio communication system that employs analog feedback that feeds back channel information measured by a user terminal to a base station using an analog transmission scheme.

  In recent years, digital transmission systems have become mainstream in wireless communication. A wireless communication apparatus that employs a digital transmission system performs quantization, binary coding, and symbol mapping signal processing on analog transmission target data when generating a transmission signal from an analog value.

  Here, quantization is a process of approximately replacing an analog value that is a continuous quantity with a discrete value such as an integer. The binary coding is a process for converting a discrete value obtained by quantization into a binary number (that is, a bit string). Symbol mapping is a process of converting a bit string obtained by binary coding into a transmission symbol (that is, digital modulation).

  Since the above-described digital transmission method can apply error correction codes and the like, it has high resistance to transmission channel noise and interference, but it is necessary to increase the transmission bit length in order to increase the resolution of transmission target data. There is a problem that capacity is tight. On the other hand, if the channel capacity is refrained and set to a short bit length, even when the channel quality is improved and the channel capacity is sufficient, the channel capacity cannot be fully utilized, and there is a problem that the resolution is lowered.

  In recent years, as disclosed in Non-Patent Document 1, analog feedback in which channel information (CSI) measured by a user terminal is fed back to a base station by an analog transmission scheme has been studied. Here, the “analog transmission method” is an operation in which measured channel information is directly converted into a transmission signal and transmitted without performing quantization or binary coding.

Chiu, E .; Ho, P .; Jae Hyung Kim, “Performance of analog feedback in closed-loop transmit diversity systems”, Wireless Communications and Networking Conference, 2006. IEEE, pages 1227-1232.

  In the CSI transfer based on the analog feedback described above, transmission errors due to uplink noise and interference cannot be corrected, and the reliability of CSI received by the base station depends on channel quality (noise level and the like). Therefore, for example, in closed loop control introduced in multiple input multiple output (MIMO) communication, transmission signal weighting processing (“precoding”) based on CSI as received by the base station is performed. If this is done, not only the transmission performance cannot be exhibited, but in some cases, the transmission signal may be significantly degraded.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a wireless communication apparatus that suppresses deterioration of a transmission signal in a wireless communication apparatus that receives channel information by analog feedback.

  One aspect of a wireless communication apparatus according to the present invention is a wireless communication apparatus that communicates with a subordinate radio communication apparatus, and the channel quality of a channel used for feedback of a signal from the subordinate radio communication apparatus And a controller that performs scheduling for allocating radio resources to the subordinate radio communication devices in consideration of the estimated channel quality, and the control unit determines the signal based on the estimated channel quality. It is determined whether or not the subordinate radio communication apparatus that has fed back is to be subjected to spatial multiplexing communication, and when the subordinate radio communication apparatus is to be subject to spatial multiplexing communication, the spatial multiplexing communication is performed with respect to the subordinate radio communication apparatus. Schedule to do.

  In one aspect of the wireless communication apparatus according to the present invention, the control unit sets a threshold value for determining whether the channel quality is good or not, and feeds back the signal when the estimated channel quality is equal to or higher than the threshold value. The subordinate radio communication apparatus is the target of the spatial multiplexing communication.

  In one aspect of the wireless communication apparatus according to the present invention, the control unit sets and estimates a first threshold value that determines whether the channel quality is good and a second threshold value that is higher than the first threshold value. When the channel quality is equal to or higher than the second threshold value, the subordinate radio communication apparatus that has fed back the signal is set as the target of the spatial multiplexing communication, and the estimated channel quality is the first threshold value and the first threshold value. If it is between two thresholds, it is subject to spatial multiplexing communication with conditions, and the conditions are the degree of separation or orthogonality with a precoder corresponding to another subordinate radio communication device, and the spatial multiplexing communication. It is defined by whether or not at least one of the necessary degrees satisfies a specified value.

  One aspect of a wireless communication apparatus according to the present invention is a wireless communication apparatus that communicates with a subordinate radio communication apparatus, and the channel quality of a channel used for feedback of a signal from the subordinate radio communication apparatus And a control unit that corrects a modulation / coding scheme for the subordinate radio communication apparatus in consideration of the estimated channel quality, and the control unit is configured to control the signal based on the estimated channel quality. In the case of determining whether to correct the modulation / coding scheme for the subordinate radio communication apparatus that has fed back, and when correcting the modulation / coding scheme, feedback is provided from the subordinate radio communication apparatus. The modulation / coding scheme is selected so as to select a modulation / coding scheme having a transmission rate lower than the modulation / coding scheme determined based on the downlink channel quality situation. To correct the scheme.

  In one aspect of the wireless communication apparatus according to the present invention, the control unit sets a threshold value for determining whether the channel quality is good or not, and feeds back the signal when the estimated channel quality is equal to or higher than the threshold value. The modulation / coding scheme for the subordinate radio communication apparatus is not corrected.

  In one aspect of the wireless communication apparatus according to the present invention, the control unit sets and estimates a first threshold value that determines whether the channel quality is good and a second threshold value that is higher than the first threshold value. When the channel quality is equal to or higher than the second threshold value, the modulation / coding scheme for the subordinate radio communication apparatus that has fed back the signal is not corrected, and the estimated channel quality is the first threshold value. And the second threshold, the first modulation having a transmission rate lower than the modulation / coding scheme determined based on the downlink channel quality status fed back from the subordinate radio communication apparatus A second modulation / coding scheme having a transmission rate lower than that of the first modulation / coding scheme when an encoding scheme is selected and the estimated channel quality is smaller than the first threshold; Correcting the modulation and coding scheme to select.

  One aspect of a wireless communication apparatus according to the present invention is a wireless communication apparatus that communicates with a subordinate radio communication apparatus, and the channel quality of a channel used for feedback of a signal from the subordinate radio communication apparatus And a controller that corrects rank adaptation for the subordinate radio communication apparatus in consideration of the estimated channel quality, and the controller feeds back the signal based on the estimated channel quality. In addition, when determining whether to correct the rank adaptation for the subordinate radio communication apparatus, and when correcting the rank adaptation, from the number of ranks corresponding to the channel information fed back from the subordinate radio communication apparatus The rank adaptation is corrected so as to select a smaller rank number.

  In one aspect of the wireless communication apparatus according to the present invention, the control unit sets a threshold value for determining whether the channel quality is good or not, and feeds back the signal when the estimated channel quality is equal to or higher than the threshold value. The rank adaptation for the subordinate radio communication apparatus is not corrected.

  In one aspect of the wireless communication apparatus according to the present invention, the control unit sets and estimates a first threshold value that determines whether the channel quality is good and a second threshold value that is higher than the first threshold value. When the channel quality is equal to or higher than the second threshold, the rank adaptation for the subordinate radio communication apparatus that has fed back the signal is not corrected, and the estimated channel quality is the first threshold and the first threshold. 2 is selected, a first rank number smaller than the rank number corresponding to the channel information fed back from the subordinate radio communication device is selected, and the estimated channel quality is the first channel quality. Is smaller than the threshold value, the rank adaptation is corrected so as to select a second rank number smaller than the first rank number.

  One aspect of a wireless communication apparatus according to the present invention is a wireless communication apparatus that communicates with a subordinate radio communication apparatus, and the channel quality of a channel used for feedback of a signal from the subordinate radio communication apparatus And a control unit that changes a transmission mode for the subordinate radio communication apparatus in consideration of the estimated channel quality, and the control unit feeds back the signal based on the estimated channel quality. Determining whether or not to change the transmission mode for the subordinate radio communication device, and when changing the transmission mode, select a transmission mode that does not use PMI (Precoding Matrix Indicator) or channel matrix, When the transmission mode is not changed, a transmission mode using the PMI or the channel matrix is selected.

  In one aspect of the wireless communication apparatus according to the present invention, the control unit sets a threshold value for determining whether the channel quality is good or not, and feeds back the signal when the estimated channel quality is equal to or higher than the threshold value. The transmission mode for the subordinate radio communication apparatus is not changed.

  In one aspect of the wireless communication apparatus according to the present invention, the control unit sets and estimates a first threshold value that determines whether the channel quality is good and a second threshold value that is higher than the first threshold value. When the channel quality is equal to or higher than the second threshold, the transmission mode for the subordinate radio communication apparatus that has fed back the signal is not changed, and a transmission mode in closed loop MIMO or MU-MIMO is selected. If the estimated channel quality is between the first threshold value and the second threshold value, a transmission mode in open-loop MIMO is selected for the subordinate radio communication apparatus, and the estimated channel When the quality is lower than the first threshold, a transmission mode with transmission diversity is selected for the subordinate radio communication apparatus.

  One aspect of a wireless communication apparatus according to the present invention is a wireless communication apparatus that communicates with a subordinate radio communication apparatus, and the channel quality of a channel used for feedback of a signal from the subordinate radio communication apparatus And a controller that performs scheduling for allocating radio resources to the subordinate radio communication devices in consideration of the estimated channel quality, and the control unit determines the signal based on the estimated channel quality. When determining whether or not to change the priority of resource block assignment to the subordinate radio communication apparatus that has fed back, and when changing the priority of resource block assignment, to the subordinate radio communication apparatus, Relatively change the resource block allocation priority.

  In one aspect of the wireless communication device according to the present invention, the control unit sets a threshold value for determining whether the channel quality is good or not, and resources for the subordinate wireless communication device that has fed back the signal based on the threshold value Decide whether to change the priority of block allocation.

  In one aspect of the wireless communication apparatus according to the present invention, the control unit sets and estimates a first threshold value that determines whether the channel quality is good and a second threshold value that is higher than the first threshold value. When the channel quality is equal to or higher than the second threshold, the priority of the resource block allocation to the subordinate radio communication apparatus that has fed back the signal is not changed, and the estimated channel quality is the first channel quality. The priority of the resource block allocation to the subordinate radio communication apparatus is lowered to the first priority, and the estimated channel quality is the first threshold If it is smaller than the threshold, the priority of the resource block allocation to the subordinate radio communication apparatus is lowered to a second priority lower than the first priority.

  In one aspect of the wireless communication apparatus according to the present invention, the control unit dynamically adjusts the channel quality estimation interval according to the speed of change of the channel quality.

  One aspect of a signal processing control method according to the present invention is a signal processing control method in a wireless communication device that performs communication with a subordinate radio communication device, and includes a signal processing control method for a signal from the subordinate radio communication device. (A) estimating channel quality of a channel used for feedback, and (b) performing scheduling for allocating radio resources to the subordinate radio communication apparatuses in consideration of the estimated channel quality. The step (b) determines, based on the estimated channel quality, whether or not the subordinate radio communication apparatus that has fed back the signal is to be subjected to spatial multiplexing, and the spatial multiplexing communication In the case of the target, it includes a step of performing scheduling so as to perform the spatial multiplexing communication for the subordinate radio communication apparatus.

  One aspect of a signal processing control method according to the present invention is a signal processing control method in a wireless communication device that performs communication with a subordinate radio communication device, and includes a signal processing control method for a signal from the subordinate radio communication device. (A) estimating a channel quality of a channel used for feedback, and (b) correcting a modulation / coding scheme for the subordinate radio communication apparatus in consideration of the estimated channel quality. The step (b) determines whether or not to correct the modulation / coding scheme for the subordinate radio communication apparatus that has fed back the signal based on the estimated channel quality; When correcting the coding method, from the modulation / coding method determined based on the channel quality status fed back from the subordinate radio communication device Comprising the step of correcting the modulation and coding scheme as the transmission rate selects a lower modulation and coding scheme.

  One aspect of a signal processing control method according to the present invention is a signal processing control method in a wireless communication device that performs communication with a subordinate radio communication device, and includes a signal processing control method for a signal from the subordinate radio communication device. (A) estimating a channel quality of a channel used for feedback, and (b) correcting a rank adaptation for the subordinate radio communication device in consideration of the estimated channel quality, Step (b) determines, based on the estimated channel quality, whether to correct the rank adaptation for the subordinate radio communication apparatus that has fed back the signal, and to correct the rank adaptation. Is smaller than the rank number corresponding to the channel information fed back from the subordinate radio communication apparatus. There comprising the step of correcting the rank adaptation to select the number of ranks.

  One aspect of a signal processing control method according to the present invention is a signal processing control method in a wireless communication device that performs communication with a subordinate radio communication device, and includes a signal processing control method for a signal from the subordinate radio communication device. (A) estimating the channel quality of the channel used for feedback, and (b) changing the transmission mode for the subordinate radio communication device in consideration of the estimated channel quality, Step (b) determines, based on the estimated channel quality, whether to change the transmission mode for the subordinate radio communication apparatus that has fed back the signal, and to change the transmission mode. If a transmission mode that does not use PMI (Precoding Matrix Indicator) or channel matrix is selected and the transmission mode is not changed, PMI or Includes the step of selecting a transmission mode using the channel matrix.

  One aspect of a signal processing control method according to the present invention is a signal processing control method in a wireless communication device that performs communication with a subordinate radio communication device, and includes a signal processing control method for a signal from the subordinate radio communication device. (A) estimating channel quality of a channel used for feedback, and (b) performing scheduling for allocating radio resources to the subordinate radio communication apparatuses in consideration of the estimated channel quality. The step (b) determines, based on the estimated channel quality, whether or not to change the priority of resource block allocation to the subordinate radio communication apparatus that has fed back the signal, and the resource When changing the priority of block allocation, resource block allocation to the subordinate radio communication apparatus Comprising the step of relatively changing the Sakido.

  ADVANTAGE OF THE INVENTION According to this invention, the radio | wireless communication apparatus which suppressed degradation of the transmission signal can be obtained.

It is a block diagram of the LTE system which concerns on Embodiment 1- Embodiment 3. FIG. It is a block diagram of UE according to Embodiment 1 to Embodiment 3. It is a block diagram of eNB which concerns on Embodiment 1- Embodiment 3. FIG. It is a figure which shows the protocol stack of the radio | wireless interface in a LTE system. It is a block diagram of the radio | wireless frame used with a LTE system. 6 is a flowchart for explaining a correction of scheduling based on an estimated value of channel quality in the first embodiment. It is a flowchart explaining the operation | movement which determines determination of the estimated channel quality in two steps. 10 is a flowchart for explaining adaptive modulation correction based on an estimated value of channel quality in the second embodiment. 10 is a flowchart illustrating correction of rank adaptation based on an estimated value of channel quality in the third embodiment. 10 is a flowchart illustrating an operation for changing a transmission mode based on an estimated value of channel quality in the fourth embodiment. It is a flowchart explaining the operation | movement which determines determination of the estimated channel quality in two steps. It is a figure explaining subband feedback. It is a figure which shows an example of scheduling. FIG. 10 is a flowchart for explaining scheduling correction based on an estimated value of channel quality in the fifth embodiment. It is a figure which shows an example of correction | amendment of scheduling. It is a flowchart explaining the method to adjust the space | interval of channel estimation dynamically.

(Introduction)
Prior to the description of the embodiments of the present invention, an LTE (Long Term Evolution) system standardized by 3GPP (3rd Generation Partnership Project) will be described.

  FIG. 1 is a configuration diagram of an LTE system. As shown in FIG. 1, the LTE system includes a plurality of UEs (User Equipment) 100, an E-UTRAN (Evolved-UMTS Terrestria 1 Radio Access Network) 10, and an EPC (Evolved Packet Core) 20. The E-UTRAN 10 corresponds to a radio access network, and the EPC 20 corresponds to a core network. The E-UTRAN 10 and the EPC 20 constitute an LTE system network.

  The UE 100 is a mobile communication device, and performs wireless communication with a connection destination cell (serving cell). UE100 is corresponded to a user terminal.

  The E-UTRAN 10 includes a plurality of eNBs 200 (Evolved Node-B). The eNB 200 corresponds to a base station. The eNB 200 manages one or a plurality of cells, and performs radio communication with the UE 100 (a subordinate radio communication device) that has established a connection with a cell managed by the eNB 200. Note that “cell” is used as a term indicating a minimum unit of a radio communication area, and also as a term indicating a function of performing radio communication with the UE 100.

  The eNB 200 has, for example, a radio resource management (RRM) function, a user data routing function, and a measurement control function for mobility control and scheduling.

  The EPC 20 includes a plurality of MME (Mobility Management Entity) / S-GW (Serving-Gateway) 300.

  The MME is a network node that performs various types of mobility control for the UE 100, and corresponds to a control station. The S-GW is a network note that performs user data transfer control, and corresponds to an exchange. EPC20 comprised by MME / S-GW300 accommodates eNB200.

  The eNB 200 is connected to each other via the interface X2. The eNB 200 is connected to the MME / S-GW 300 via the interface X1.

  FIG. 2 is a block diagram illustrating a configuration of the UE 100. As shown in FIG. 2, the UE 100 includes a plurality of antennas 101, a radio transceiver 110, a user interface 120, a GNSS (Global Navigation Satellite System) receiver 130, a battery 140, a memory 150, and a processor 160. Have. Note that the UE 100 may not have the GNSS receiver 130. Further, the memory 150 may be integrated with the processor 160, and this set (that is, a chip set) may be used as the processor 160 ′.

  The plurality of antennas 101 and the wireless transceiver 110 are used for transmitting and receiving wireless signals. The radio transceiver 110 includes a transmission unit 111 that converts a baseband signal (transmission signal) output from the processor 160 into a radio signal and transmits the radio signal from a plurality of antennas 101. The radio transceiver 110 includes a receiving unit 112 that converts radio signals received by the plurality of antennas 101 into baseband signals (received signals) and outputs the baseband signals to the processor 160.

  The user interface 120 is an interface with a user who owns the UE 100, and includes, for example, a display, a microphone, a speaker, and various buttons. The user interface 120 receives an operation from the user and outputs a signal indicating the content of the operation to the processor 160.

  The GNSS receiver 130 receives a GNSS signal and outputs the received signal to the processor 160 in order to obtain location information indicating the geographical location of the UE 100. The battery 140 stores power to be supplied to each block of the UE 100.

  The memory 150 stores a program executed by the processor 160 and information used for processing by the processor 160. The processor 160 includes a signal processing unit 161 that performs signal processing such as modulation / demodulation and encoding / decoding of a baseband signal, and a control unit 162 that executes various programs by executing programs stored in the memory 150. Contains.

  Here, as will be described later, since the downlink channel information (CSI) measured by the UE 100 is transmitted to the eNB 200 by analog feedback, the signal processing unit 161 includes an analog transmission processing unit in addition to the digital transmission processing unit. ing.

  The digital transmission processing unit generates a transmission signal by a digital transmission method according to the current 3GPP standard.

  The analog transmission processing unit generates a transmission signal by an analog transmission method.

  The processor 160 may further include a codec that performs encoding / decoding of an audio / video signal. The processor 160 executes various controls described later.

  FIG. 3 is a block diagram illustrating a configuration of the eNB 200. As illustrated in FIG. 3, the eNB 200 includes a plurality of antennas 201, a radio transceiver 210, a network interface 220, a memory 230, and a processor 240. The memory 230 and the processor 240 constitute a base station side control unit.

  The plurality of antennas 201 and the wireless transceiver 210 are used for transmitting and receiving wireless signals. The radio transceiver 210 includes a transmission unit 211 that converts a baseband signal (transmission signal) output from the processor 240 into a radio signal and transmits the radio signal from a plurality of antennas 201. The wireless transceiver 210 includes a reception unit 212 that converts wireless signals received by the plurality of antennas 201 into baseband signals (reception signals) and outputs the baseband signals to the processor 240.

  The network interface 220 is connected to the adjacent eNB 200 via the interface X2 (FIG. 1), and is connected to the MME / S-GW 300 via the interface X1 (FIG. 1). The network interface 220 is used for communication performed on the interface X2 and communication performed on the interface X1.

  The memory 230 stores a program executed by the processor 240 and information used for processing by the processor 240. The processor 240 includes a signal processing unit 241 that performs signal processing such as modulation / demodulation and encoding / decoding of a baseband signal, and a control unit 242 that executes various programs by executing a program stored in the memory 230. Contains. The processor 240 executes various controls described later.

  Here, the eNB 200 receives downlink channel information (CSI) transmitted by an analog transmission scheme. The signal processing unit 241 of the eNB 200 has a function of detecting downlink channel information transmitted by an analog transmission method. More specifically, the signal processing unit 241 of the eNB 200 has a function of equalizing the received analog signal with uplink channel information obtained from the reference signal and detecting a value indicating the equalized analog signal as target data. ing.

  FIG. 4 is a diagram illustrating a protocol stack of a radio interface in the LTE system. As shown in FIG. 4, the radio interface protocol is divided into layers 1 to 3 of the OSI reference model, and layer 1 is a physical (PHY) layer. Layer 2 includes a MAC (Media Access Control) layer, an RLC (Radio Link Control) layer, and a PDCP (Packet Data Convergence Protocol) layer. Layer 3 includes an RRC (Radio Resource Control) layer.

  The physical layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data is transmitted between the physical layer of the UE 100 and the physical layer of the eNB 200 via a physical channel.

  The MAC layer performs data priority control, retransmission processing by hybrid ARQ (HARQ), and the like. Data is transmitted via the transport channel between the MAC layer of the UE 100 and the MAC layer of the eNB 200. The MAC layer of the eNB 200 includes a scheduler that determines an uplink / downlink transport format (transport block size, modulation / coding scheme (MCS)) and an allocation source block.

  The RLC layer transmits data to the RLC layer on the receiving side using functions of the MAC layer and the physical layer. Data is transmitted between the RLC layer of the UE 100 and the RLC layer of the eNB 200 via a logical channel.

  The PDCP layer performs header compression / decompression and encryption / decryption.

  The RRC layer is defined only in the control plane. Control messages (RRC messages) for various settings are transmitted between the RRC layer of the UE 100 and the RRC layer of the eNB 200. The RRC layer controls logical channels, transport channels, and physical channels in response to radio bearer establishment, re-establishment, and release. When there is an RRC connection between the RRC of the UE 100 and the RRC of the eNB 200, the UE 100 is in a connected state (RRC connected state). Otherwise, the UE 100 is in an idle state (RRC idle state).

  A NAS (Non-Access Stratum) layer located above the RRC layer performs session management and mobility management.

  FIG. 5 is a configuration diagram of a radio frame used in the LTE system. In the LTE system, OFDMA (Orthogonal Frequency Division Multiplexing Access) is applied to the downlink, and SC-FDMA (Single Carrier Frequency Division Multiple Access) is applied to the uplink.

  As shown in FIG. 5, the radio frame is composed of 10 subframes arranged in the time direction, and each subframe is composed of two slots arranged in the time direction. The length of each subframe is lmsec, and the length of each slot is 0.5 msec. Each subframe includes a plurality of resource blocks (RB) in the frequency direction and includes a plurality of symbols in the time direction. The resource block includes a plurality of subcarriers in the frequency direction. A radio resource unit configured by one subcarrier and one symbol is referred to as a resource element (RE).

  Among radio resources allocated to the UE 100, frequency resources can be specified by resource blocks, and time resources can be specified by subframes (or slots).

  In the downlink, the section of the first few symbols of each subframe is a control region mainly used as a physical downlink control channel (PDCCH) for transmitting a control signal. The remaining section of each subframe is an area that can be used as a physical downlink shared channel (PDSCH) mainly for transmitting user data.

  The PDCCH carries a control signal. The control signal includes, for example, uplink SI (Scheduling Information), downlink SI, and TPC bits. The uplink SI is information indicating uplink radio resource allocation, and the downlink SI is information indicating downlink radio resource allocation. The TPC bit is information instructing increase / decrease in uplink transmission power. These pieces of information are referred to as downlink control information (DCI).

  The PDSCH carries control signals and / or user data. For example, the downlink data area may be allocated only to user data, or may be allocated so that user data and control signals are multiplexed.

  In the downlink, cell-specific reference signals (CRS) and channel information reference signals (CSI-RS) are distributed and provided in each subframe. Each of CRS and CSI-RS is configured by a predetermined orthogonal signal sequence. The eNB 200 transmits CRS and CSI-RS from each of the plurality of antennas 201.

  In the uplink, both ends in the frequency direction in each subframe are control regions mainly used as a physical uplink control channel (PUCCH) for transmitting a control signal. Further, the central portion in the frequency direction in each subframe is an area that can be used as a physical uplink shared channel (PUSCH) mainly for transmitting user data.

  The PUCCH carries a control signal. The control signal is, for example, CQI (Channel Quality Indicator), PMI (Precoding Matrix Indicator), RI (Rank Indicator), SR (Scheduling Request), ACK / NACK, or the like.

  CQI is an index indicating downlink channel quality, and is used to determine a recommended modulation scheme and coding rate to be used for downlink transmission. The PMI is an index indicating a precoder matrix that is preferably used for downlink transmission. The RI is an index indicating the number of layers (number of ranks, number of streams) that can be used for downlink transmission. SR is information for requesting allocation of uplink radio resources (resource blocks). ACK / NACK is information indicating whether or not a signal transmitted via a downlink physical channel (for example, PDSCH) has been successfully decoded.

  CQI, PMI, and RI correspond to channel information (CSI: Channel Sate Information) obtained by UE 100 performing channel estimation using a downlink reference signal (CRS and / or CSI-RS).

  The PUSCH carries control signals and / or user data. For example, the uplink data area may be allocated only to user data, or may be allocated so that user data and control signals are multiplexed.

  In the uplink, a predetermined symbol of each subframe is provided with a sounding reference signal (SRS) and a demodulation reference signal (DMRS). Each of SRS and DMRS is configured by a predetermined orthogonal signal sequence.

  The embodiments will be described below by taking the application to the LTE system described with reference to FIGS. 1 to 5 as an example.

(Embodiment 1)
The UE 100 feeds back the measured downlink channel information (CSI) to the eNB 200 by an analog transmission method (analog feedback). However, as described above, the UE 100 cannot correct a transmission error due to uplink noise or interference, The reliability of CSI received by the eNB 200 depends on channel quality (noise level, etc.).

  In the present embodiment, eNB 200 estimates channel quality of the uplink channel used for CSI feedback, and performs appropriate scheduling for the UE in downlink communication based on the estimated channel quality.

  CSI feedback from the UE 100 is normally performed using a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH), and the eNB 200 estimates these channel qualities.

  FIG. 6 is a flowchart for explaining the scheduling operation based on the channel quality estimation value in the first embodiment.

  As illustrated in FIG. 6, when receiving the downlink channel CSI fed back from the UE 100, the eNB 200 estimates the channel quality of the uplink channel used for CSI feedback (step S1). The channel quality is defined by SINR (Signal to Interference plus Noise Ratio) or SNR (signal to noise ratio), and PUCCH and PUSCH channel quality uses sounding reference signal (SRS) and / or demodulation reference signal (DMRS). Can be estimated. In addition, regarding PUCCH, it is also conceivable to estimate the channel quality from the crowded situation of allocated users managed by the eNB 200 itself.

  Next, the estimated channel quality value is compared with a predetermined threshold value (referred to as threshold value 1 for convenience) (step S2). If the estimated channel quality value is smaller than threshold value 1, the process proceeds to step S4. If the estimated channel quality value is equal to or greater than the threshold 1, the process proceeds to step S3. When SINR is used as the channel quality, the threshold value 1 is set to 5 dB, for example.

  Here, the LTE system has a MU-MIMO (Multi-User-MIMO) function for simultaneously transmitting different data to a plurality of UEs by generating a plurality of signal waves that do not interfere with each other by beam forming. . When the process proceeds to step S3, that is, for the UE whose estimated channel quality value is equal to or greater than the threshold value 1, it is set as the target of MU-MIMO, and a MU-MIMO precoder is generated. -Perform MIMO.

  On the other hand, if the process proceeds to step S4, that is, the UE whose estimated channel quality value is less than the threshold value 1 is not subject to MU-MIMO.

  That is, when downlink channel information (CSI) is fed back by analog transmission, if the quality of a channel (PUCCH or PUSCH) used for feedback is poor, the reliability (accuracy) of the received CSI is low, and based on the CSI When MU-MIMO is performed, transmission performance is degraded. Therefore, MU-MIMO is not targeted for UEs that have fed back CSI using poor quality channels, but only for UEs that have fed back CSI using good quality channels. By making it a target, it is possible to avoid a decrease in transmission performance.

  In the above description, the configuration for determining whether or not to perform MU-MIMO based on the channel quality estimation value has been described. However, the application of the present embodiment is not limited to MU-MIMO and may be spatial multiplexing. For example, it may be applied to SDMA (space division multiple access). SDMA can also transmit different data simultaneously to multiple UEs using the same channel.

(Modification)
In the first embodiment described above, the configuration for determining whether or not to perform spatial multiplexing communication based on the channel quality estimation value has been described, but the estimation of the estimated channel quality is performed step by step using a plurality of threshold values. It is good also as a structure to determine to.

  For example, two high and low threshold values are set, and a UE that has fed back CSI on a channel having a quality higher than the higher threshold value is unconditionally targeted for MU-MIMO, and the quality between the two threshold values. For UEs that have fed back CSI on the other channel, MU-MIMO is subject to conditions, and for UEs that have fed back CSI on lower quality channels than the lower threshold, it is subject to MU-MIMO. You may take the structure of not.

  An example of this will be described with reference to FIG. FIG. 7 is a flowchart for explaining the operation of setting two types of channel quality thresholds and determining the estimated channel quality in two stages.

  As illustrated in FIG. 7, when receiving the CSI fed back from the UE 100, the eNB 200 estimates the channel quality of the channel used for CSI feedback (step S11).

  Next, the estimated channel quality value is compared with a predetermined first threshold value (referred to as threshold value 2 for convenience) (step S12). If the estimated channel quality value is smaller than the threshold value 2, the process proceeds to step S15. If the estimated channel quality value is equal to or greater than the threshold 2, the process proceeds to step S13. When SINR is used as the channel quality, the threshold 2 is set to 5 dB, for example.

  And when it progresses to step S15, ie, UE with which the value of the estimated channel quality is less than threshold value 2, it is not made into the object of MU-MIMO.

  On the other hand, when the process proceeds to step S13, that is, when the estimated channel quality value is greater than or equal to the threshold value 2, the estimated channel quality value is compared with a predetermined second threshold value (for convenience, referred to as threshold value 3). If the estimated channel quality value is smaller than the threshold 3, the process proceeds to step S16. If the estimated channel quality value is equal to or greater than the threshold 3, the process proceeds to step S14.

  When SINR is used as the channel quality, the threshold value 3 is set to 8 dB, for example.

  When the process proceeds to step S16, that is, for the UE whose estimated channel quality value is less than the threshold 3, it is conditionally set as a target for MU-MIMO.

  Here, the condition is, for example, whether or not at least one of the degree of separation or orthogonality with a precoder corresponding to another UE that is a target of MU-MIMO and the required degree of MU-MIMO satisfies a specified value. Defined by

  Note that the degree of necessity of MU-MIMO can be defined by, for example, the number of remaining resources. If there are many remaining resources, it is determined that the need for MU-MIMO is small, and the estimated channel quality UE whose value is less than threshold 3 is not subject to MU-MIMO, and if there are not enough resources, it is determined that MU-MIMO is necessary, and the estimated channel quality value is less than threshold 3 UE to perform is set as a target of MU-MIMO. Note that the amount of remaining resources may be determined based on, for example, a predetermined value of the predetermined resource.

  In addition, when the degree of separation or orthogonality with the precoder corresponding to another UE to be subjected to MU-MIMO is small, it is determined that it is difficult to separate signals from other UEs, and the estimated channel quality UEs whose values are less than threshold 3 are not subject to MU-MIMO, and when the degree of separation or orthogonality is large, UEs whose estimated channel quality values are less than threshold 3 are set as targets for MU-MIMO. To do. Note that the degree of separation or orthogonality with the precoder may be determined based on, for example, a predetermined value of separation or orthogonality that is determined in advance.

  On the other hand, when the process proceeds to step S14, that is, for the UE whose estimated channel quality value is equal to or greater than the threshold 3, the MU-MIMO codebook is generated unconditionally as a MU-MIMO target. MU-MIMO.

  In this way, by adopting a configuration in which the estimated channel quality is determined stepwise using a plurality of threshold values, the channel quality can be classified and dealt with more finely.

  Note that the scheduling based on the channel quality estimation value described with reference to FIGS. 6 and 7 is an operation performed by the control unit 242 of the processor 240 of the eNB 200.

(Embodiment 2)
In the first embodiment and the modification thereof described above, the eNB 200 estimates the channel quality of the channel used for CSI feedback and performs scheduling based on the estimated channel quality. It is good also as a structure which determines whether the encoding system (MCS: Modulation and Coding Scheme) is correct | amended.

  FIG. 8 is a flowchart for explaining the operation of correcting the modulation / coding scheme based on the estimated value of channel quality in the second embodiment.

  As illustrated in FIG. 8, upon receiving CSI fed back from the UE 100, the eNB 200 estimates the channel quality of the channel used for CSI feedback (step S21).

  Next, the estimated channel quality value is compared with a predetermined threshold value (referred to as a threshold value 4 for convenience) (step S22). If the estimated channel quality value is smaller than the threshold value 4, the process proceeds to step S24. If the estimated channel quality value is equal to or greater than the threshold value 4, the process proceeds to step S23. When SINR is used as the channel quality, the threshold value 4 is set to 5 dB, for example.

  When the process proceeds to step S23, that is, for the UE whose estimated channel quality value is equal to or greater than the threshold value 4, the MCS is not corrected.

  Table 1 below shows a mapping table of channel quality status (CQI) and MCS used in the LTE system.

  In Table 1, the channel quality is divided into 16 stages, and CQI indexes from 0 to 15 are attached. Among them, the MCS is assigned to the CQI index from 1 to 15, and the MCS is not assigned to the CQI index 0.

  Also, as shown in Table 1, the modulation scheme, code rate × 1024, and transmission efficiency are stored in association with the CQI index.

  The smaller the CQI, the worse the channel quality. Table 1 shows modulation and coding schemes suitable for the channel quality represented by CQI.

  In the LTE system, when the eNB 200 receives CSI fed back from the UE 100, the corresponding modulation / coding scheme (MCS) is determined from Table 1 based on the CSI (here, CQI). For example, if the fed back CSI is 7, the modulation method is 16QAM and the code rate is 378 × 1/1024. This is a normal process when the MCS is not corrected, and the MCS determined in this way is referred to as a normal MCS.

  On the other hand, when the process proceeds to step S24, that is, for the UE whose estimated channel quality value is less than the threshold value 4, the MCS is corrected.

  That is, when CSI is fed back by analog transmission, if the quality of the channel used for feedback is poor, the reliability (accuracy) of the received CSI is low, and determining the MCS based on the CSI causes a decrease in transmission performance. . Therefore, for a UE that has fed back CSI using a channel with poor quality, it is possible to avoid a decrease in transmission performance by selecting an MCS having a transmission rate lower than that of a normal MCS.

  For example, if the fed back CSI, here CQI is 5, in a normal process, the modulation method is QPSK and the code rate is set to 449 × 1/1024, but the estimated channel quality value is the threshold 4 For UEs corresponding to less than 1, the modulation scheme is QPSK and the code rate is 308 × 1/1024. This is the process when the MCS is corrected. How to correct the MCS is arbitrary.

  Further, the estimated channel quality may be determined stepwise using a plurality of threshold values. For example, MCS is determined by normal processing for a UE that has set two threshold values, high and low, and CSI is fed back on a channel with a quality higher than the higher threshold, but the quality between the two thresholds For UEs that have fed back CSI on the other channel, an MCS with a lower transmission rate than normal MCS is selected, and for UEs that have fed back CSI on a channel with a lower quality than the lower threshold, Furthermore, it is good also as a structure which selects MCS with a low transmission rate. In this case, the higher threshold is set to 8 dB, for example, and the lower threshold is set to 5 dB, for example.

  In this way, by adopting a configuration in which the estimated channel quality is determined stepwise using a plurality of threshold values, the channel quality can be classified and dealt with more finely.

  Note that the determination of the necessity of MCS correction and the MCS correction based on the estimated channel quality values described with reference to FIG. 8 are operations performed by the control unit 242 of the processor 240 of the eNB 200.

(Embodiment 3)
In the second embodiment described above, the eNB 200 estimates the channel quality of the channel used for CSI feedback, and determines whether to correct the modulation / coding scheme based on the estimated channel quality However, it may be configured to correct the rank adaptation.

  That is, in MIMO communication, high-speed transmission is possible by increasing the number of ranks (number of streams, number of layers), but when CSI is fed back by analog transmission, if the quality of the channel used for feedback is poor, The reliability (accuracy) of the received CSI is low, and if the rank is determined based on the CSI, the transmission performance is degraded. Therefore, for UEs that have fed back CSI using a channel with poor quality, transmission is performed at a rank number that is one step lower than the rank number determined based on CSI, for example. A decrease can be avoided.

  FIG. 9 is a flowchart for explaining the operation of correcting rank adaptation based on the estimated value of channel quality in the third embodiment.

  As illustrated in FIG. 9, upon receiving CSI fed back from the UE 100, the eNB 200 estimates the channel quality of the channel used for CSI feedback (step S31).

  Next, the estimated channel quality value is compared with a predetermined threshold value (referred to as threshold value 5 for convenience) (step S32). If the estimated channel quality value is smaller than the threshold value 5, the process proceeds to step S34. If the estimated channel quality value is equal to or greater than the threshold value 5, the process proceeds to step S33. When SINR is used as the channel quality, the threshold value 5 is set to 5 dB, for example.

  When the process proceeds to step S33, that is, for the UE whose estimated channel quality value is equal to or greater than the threshold value 5, the rank is determined by normal processing without correcting the rank adaptation.

  That is, taking RI as an example, 1 to 8 are defined as index values, and the number of ranks associated with the index value increases as the index value increases. Transmitting with is a normal process when rank adaptation is not corrected.

  On the other hand, when the process proceeds to step S34, that is, for the UE whose estimated channel quality value is less than the threshold value 5, the rank adaptation is corrected to determine the rank.

  For example, if the RI index value fed back from the UE for determining the rank is 5, in normal processing, transmission is performed with the number of ranks corresponding to the RI index value 5, but the estimated channel quality value is the threshold value 5 For the UE corresponding to less than, the RI index value is lowered by one step, for example, and transmission is performed with the number of ranks corresponding to the RI index value 4. This is the process when the rank adaptation is corrected. The number of steps of lowering the RI index value is arbitrary, and can be lowered by two or more steps.

  Further, the estimated channel quality may be determined stepwise using a plurality of threshold values. For example, two thresholds are set, high and low, and the number of ranks is determined by a normal process for a UE that has fed back CSI on a channel having a higher quality than the higher threshold. For UEs that have fed back CSI on the quality channel, select the number of ranks corresponding to the RI index value that is one step lower, and for UEs that have fed back CSI on the channel with lower quality than the lower threshold May be configured to select the number of ranks corresponding to the RI index value that is two steps lower. In this case, the higher threshold is set to 8 dB, for example, and the lower threshold is set to 5 dB, for example.

  In this way, by adopting a configuration in which the estimated channel quality is determined stepwise using a plurality of threshold values, the channel quality can be classified and dealt with more finely.

  Note that the determination of necessity of rank adaptation correction and the rank adaptation correction based on the estimated channel quality values described with reference to FIG. 9 are operations performed by the control unit 242 of the processor 240 of the eNB 200.

  In the above description, the configuration in which rank adaptation is performed using the fed-back RI has been described. However, rank adaptation may be corrected based on the CSI or the channel matrix that is fed back without being limited to the RI.

(Embodiment 4)
In the first to third embodiments described above, the eNB 200 estimates the channel quality of the channel used for CSI feedback, and determines whether to set the MU-MIMO target based on the estimated channel quality. Although it is configured to determine whether or not to correct the encoding method and whether or not to correct the rank adaptation, a configuration to change the transmission mode based on the channel quality of the channel used for CSI feedback It is also good.

  In the LTE system, there are transmission modes such as transmission diversity and open loop MIMO. Transmission diversity does not depend on CSI from the UE, and open-loop MIMO has a low dependency on CSI from the UE, and both have the characteristics of good transmission stability.

  When CSI is fed back by analog transmission, if the quality of the channel used for feedback is poor, the reliability (accuracy) of the received CSI is low. In such a case, if downlink transmission is performed with closed-loop MIMO or MU-MIMO, transmission performance is degraded. Therefore, when there is a possibility that the accuracy of CSI is low, transmission performance can be maintained by performing downlink transmission with transmission diversity that does not depend on CSI or open-loop MIMO that has low dependency on CSI.

  That is, transmission diversity and open-loop MIMO are transmission modes that do not use PMI (or channel matrix), and are designed to always obtain average characteristics in terms of probability. On the other hand, closed-loop MIMO is a transmission mode that is dynamically optimized using PMI (or channel matrix). If transmission is performed according to PMI (or channel matrix) with low reliability, CSI accuracy is low. There is a possibility that the transmission performance is lower than that of transmission diversity or open-loop MIMO.

  Note that the transmission mode that is dynamically optimized using the PMI (or channel matrix) is a transmission mode that enables the setting of feeding back the PMI or channel matrix from the UE by setting the transmission mode. It may be a transmission mode in which a precoder used for transmission is selected from a plurality of precoders and transmitted when transmitting by the number of streams.

  In addition, as a transmission mode that does not use the PMI (or channel matrix), a transmission mode that does not allow the setting of feeding back the PMI or channel matrix from the UE by setting the transmission mode, or transmission with a certain number of transmission streams In this case, a transmission mode may be used in which transmission is performed using a predetermined precoder (or a combination of predetermined plural precoders).

  FIG. 10 is a flowchart for explaining the operation of changing the transmission mode based on the estimated value of channel quality in the fourth embodiment.

  As illustrated in FIG. 10, when receiving the CSI fed back from the UE 100, the eNB 200 estimates the channel quality of the channel used for CSI feedback (step S41).

  Next, the estimated channel quality value is compared with a predetermined threshold value (referred to as threshold value 6 for convenience) (step S42). If the estimated channel quality value is smaller than threshold value 6, the process proceeds to step S44. If the estimated channel quality value is equal to or greater than the threshold 6, the process proceeds to step S43. When SINR is used as the channel quality, the threshold value 6 is set to 5 dB, for example.

  When the process proceeds to step S43, that is, for the UE whose estimated channel quality value is equal to or greater than the threshold value 6, normal processing, that is, transmission using closed loop MIMO or MU-MIMO depending on CSI is performed. When closed-loop MIMO is applied to SU-MIMO (Single-User-MIMO), the data rate can be improved, and MU-MIMO has an advantage that resources can be saved when there are few resources.

  On the other hand, when the process proceeds to step S44, that is, for the UE whose estimated channel quality value is less than the threshold 6, transmission is performed with transmission diversity or open loop MIMO. As a result, even when there is an error between the fed back downlink CSI and the actual CSI, that is, even when the reliability (accuracy) of the fed back CSI is low, the transmission performance of the downlink transmission can be maintained. .

(Modification)
In the above-described fourth embodiment, the configuration in which the transmission mode is changed based on the channel quality estimation value has been described. However, the estimated channel quality may be determined stepwise using a plurality of threshold values. good.

  For example, for a UE that has set two thresholds, high and low, and has fed back CSI on a channel having a quality higher than the higher threshold, normal processing, that is, transmission in closed-loop MIMO or MU-MIMO, is performed. Do. For UEs that have fed back CSI on a channel with quality between the two thresholds, transmission is performed in open-loop MIMO, and UEs that have fed back CSI on a channel with lower quality than the lower threshold On the other hand, a configuration of performing transmission with transmission diversity may be adopted.

  An example thereof will be described with reference to FIG. FIG. 11 is a flowchart for explaining the operation of setting two types of channel quality thresholds and determining the estimated channel quality in two stages.

  As illustrated in FIG. 11, when receiving the CSI fed back from the UE 100, the eNB 200 estimates the channel quality of the channel used for CSI feedback (step S51).

  Next, the estimated channel quality value is compared with a predetermined first threshold value (referred to as threshold value 7 for convenience) (step S52). If the estimated channel quality value is smaller than the threshold value 7, the process proceeds to step S55. If the estimated channel quality value is equal to or greater than the threshold value 7, the process proceeds to step S53. When SINR is used as the channel quality, the threshold 7 is set to 5 dB, for example.

  And when it progresses to step S55, ie, with respect to UE in which the value of the estimated channel quality is less than the threshold value 7, transmission by transmission diversity is performed. The transmit diversity has a maximum throughput lower than that of the open loop MIMO, but does not depend on CSI and is excellent in terms of robustness. Therefore, even when the reliability (accuracy) of the fed back CSI is considerably low, the transmission diversity is constant. Transmission / reception performance can be secured. That is, it is possible to prevent the performance from being deteriorated as compared with transmission using closed-loop MIMO according to CSI with low reliability.

  On the other hand, when the process proceeds to step S53, that is, when the estimated channel quality value is greater than or equal to the threshold value 7, the estimated channel quality value is compared with a predetermined second threshold value (referred to as a threshold value 8 for convenience). If the estimated channel quality value is smaller than the threshold value 8, the process proceeds to step S56. If the estimated channel quality value is equal to or greater than the threshold value 8, the process proceeds to step S54.

  When SINR is used as the channel quality, the threshold value 8 is set to 8 dB, for example.

  When the process proceeds to step S56, that is, for the UE whose estimated channel quality value is less than the threshold value 8, transmission by open loop MIMO is performed.

  On the other hand, if the process proceeds to step S54, that is, if the estimated channel quality value is greater than or equal to the threshold value 8, normal processing, that is, transmission using closed-loop MIMO or MU-MIMO is performed.

  In this way, by adopting a configuration in which the estimated channel quality is determined stepwise using a plurality of threshold values, the channel quality can be classified and dealt with more finely.

  Note that the determination of whether or not to perform spatial multiplexing communication and the transmission mode selection operation based on the channel quality estimation value described with reference to FIGS. 10 and 11 are operations performed by the control unit 242 of the processor 240 of the eNB 200.

(Embodiment 5)
In the first embodiment, as an example of performing scheduling based on the estimated channel quality, the configuration for determining whether to perform spatial multiplexing communication based on the estimated value of channel quality has been described. However, as an example of scheduling, A configuration may be adopted in which the priority of resource block (RB) allocation is changed.

  That is, as a method of feeding back CSI from the UE, for example, wideband feedback that feeds back one CSI value for the entire system band of 10 MHz and 50 resource blocks, and one system band (10 MHz and 50 resource blocks) For example, there is subband feedback in which CSI values are fed back for each subband.

  In subband feedback, generally, a frequency resource with good characteristics is identified for each UE based on CSI fed back from each UE on the eNB side, and the frequency resource is preferentially allocated to each UE. Thus, scheduling for improving the overall performance is performed.

  FIG. 12 schematically shows subband feedback, showing a configuration in which one system band is divided into two subbands every six resource blocks, with the horizontal axis representing the time axis and the vertical axis representing the frequency axis. .

  In FIG. 12, resource blocks RB0 to RB5 are defined as subband SB0 and resource blocks RB6 to RB11 are defined as subband SB1 in one system band.

  An example of such scheduling based on subband feedback is shown in FIG. 13. For example, in the system band T1, resource blocks RB0 to RB3 are allocated to the first UE, and resource blocks RB4 to RB7 are allocated. Assigned to the second UE, resource blocks RB8 to RB11 are assigned to the first UE. The distribution of resource blocks in this way is a result of scheduling, which is a result of specifying and preferentially assigning frequency resources with good characteristics for each UE.

  In this way, frequency resources with good characteristics are allocated to each UE by scheduling, but the reliability (accuracy) of CSI received by the eNB varies from subband to subband if the quality of the channel that feeds back CSI is poor. May occur and appropriate frequency resources cannot be allocated, resulting in a decrease in overall performance.

  Thus, performance degradation can be suppressed by changing the resource block allocation priority based on the channel quality estimated on the eNB side.

  FIG. 14 is a flowchart for explaining an operation for correcting scheduling based on an estimated value of channel quality in the fifth embodiment.

  As illustrated in FIG. 14, upon receiving CSI (CSI for each subband) fed back from the UE 100, the eNB 200 estimates the channel quality of the channel used for CSI feedback (step S61). Note that the eNB 200 performs resource block allocation for each UE by performing, for example, PF scheduling based on the fed back CSI.

  Next, the estimated channel quality value is compared with a predetermined threshold value (referred to as a threshold value 9 for convenience) (step S62). If the estimated channel quality value is smaller than the threshold value 9, the process proceeds to step S64. If the estimated channel quality value is greater than or equal to the threshold value 9, the process proceeds to step S63. When SINR is used as the channel quality, the threshold value 9 is set to 5 dB, for example.

  When the process proceeds to step S63, that is, for the UE whose estimated channel quality value is equal to or greater than the threshold value 9, the resource block allocation priority is maintained as previously set (the scheduling is not corrected). ).

  On the other hand, when the process proceeds to step S64, that is, for the UE whose estimated channel quality value is less than the threshold 9, the resource block allocation priority is lowered (scheduling is corrected).

  For example, in the scheduling example shown in FIG. 13, when the feedback of the subband including the resource blocks RB0 to RB3 is performed from the first UE, if the quality of the uplink channel used for CSI feedback is poor, The allocation priority of the resource block in this subband is lowered, the priority of the second UE is increased, or the priority of the second UE is relatively increased.

  Then, by recalculating the priority for all resource blocks RB and correcting the scheduling, it is possible to suppress a decrease in performance.

  FIG. 15 shows an example of the corrected scheduling. As shown in FIG. 15, in the corrected scheduling, resource blocks RB0 to RB3 are allocated to the second UE.

  An example of scheduling is PF (Proportional Fairness) scheduling. In PF scheduling, the RF metric corresponds to the priority. Increasing the priority means increasing the RF metric, and decreasing the priority means decreasing the RF metric.

  Further, in the above description, it has been described that the resource block allocation priority is lowered for a UE whose estimated channel quality value falls below a predetermined threshold. However, the estimated channel quality value is a predetermined value. It is also possible to increase the resource block allocation priority for UEs that fall above the threshold. Since the priority is a relative value, increasing the priority can also increase the overall performance as a result.

  Also in this embodiment, the estimated channel quality may be determined stepwise using a plurality of threshold values. For example, for a UE that has set two high and low thresholds and fed back CSI on a channel with a higher quality than the higher threshold, the resource block allocation priority is maintained as previously set. Yes (does not correct scheduling), but lowers priority by one step for UEs that have fed back CSI on a channel of quality between two thresholds. And it is good also as a structure which lowers a priority two steps | paragraphs with respect to UE which has fed back CSI by the channel whose quality is lower than a lower threshold value. In this case, the higher threshold is set to 8 dB, for example, and the lower threshold is set to 5 dB, for example. Note that it goes without saying that even in the configuration in which the determination is performed step by step using a plurality of threshold values, the priority may be increased step by step based on the threshold values.

  In this way, by adopting a configuration in which the estimated channel quality is determined stepwise using a plurality of threshold values, the channel quality can be classified and dealt with more finely.

  Note that the determination of whether or not to change the resource block allocation priority based on the estimated channel quality value described with reference to FIG. 14 and the correction of scheduling are operations performed by the control unit 242 of the processor 240 of the eNB 200.

(Combination of embodiments)
Combinations of the embodiments described above are also conceivable. For example, Embodiments 2 to 4 can be combined with Embodiment 5. For example, in the configuration of the second embodiment, after the MCS is determined by correcting the modulation / coding scheme for the UE whose estimated channel quality value is less than the threshold, Processing for lowering the allocation priority (correcting scheduling) of the resource block whose estimated channel quality value is less than the threshold is performed.

  Further, in the configuration of the third embodiment, after the rank is corrected by correcting the rank adaptation for the UE whose estimated channel quality value is less than the threshold, the estimated channel in the configuration of the fifth embodiment is further determined. A process of lowering the allocation priority (correcting the scheduling) of the resource block whose quality value is less than the threshold is performed.

  Further, in the configuration of the fourth embodiment, after determining transmission with transmission diversity or open-loop MIMO for a UE whose estimated channel quality value is less than the threshold, the estimation in the configuration of the fifth embodiment is further performed. The process of lowering the allocation priority (correcting scheduling) of the resource block whose channel quality value is less than the threshold is performed.

(Channel quality estimation timing)
In Embodiments 1 to 5 described above, the timing for estimating the channel quality is not particularly mentioned, but the same timing (same subframe) as the received CSI is desirable. Therefore, as shown in the flowcharts of FIGS. 6 to 11 and 14, it is desirable to perform the CSI reception simultaneously, but the CSI reception may be performed independently.

  That is, during the series of communication sessions, when channel quality is estimated periodically at regular intervals and the channel quality estimation result is used, the most recent estimation result may be used.

  For example, when CSI is periodically fed back, the channel quality may be estimated at a timing immediately before CSI is fed back. When the CSI feedback is aperiodic, the channel quality may be estimated immediately before requesting CSI from the eNB 200 to the UE 100.

  Further, when it is not necessary to perform channel estimation frequently, the channel estimation interval may be arbitrarily set. For example, the estimation interval may be set to 20 msec, and the estimation interval may be set to, for example, 10 msec, 5 msec, or 2 msec for CSI feedback from a UE having a fast transmission path change.

  Further, as described below, the estimation interval may be dynamically adjusted according to the speed of change in channel quality.

  FIG. 16 is a flowchart for explaining a method of dynamically adjusting the channel estimation interval. As shown in FIG. 16, when communication is started between the eNB 200 and the UE 100, for example, 20 msec is set as the initial estimated interval (step S81).

  Then, channel estimation is repeated at 20 msec intervals, and each time, a difference between the new estimated value and the previous (previous) estimated value is calculated, and it is determined whether or not the difference between the two exceeds 20% (step S82). . If there are three or more cases exceeding 20% within the predetermined period, the process proceeds to step S86. Otherwise, the process proceeds to step S83.

  Here, the case where it exceeds 20% within a predetermined period is more than 3 times means that it exceeds 20% within, for example, 5 times of the currently set estimation interval (within 5 time estimations). Means that the estimated interval is more than 3 times, and when the estimated interval is, for example, the default 20 msec interval, it is said that it exceeded 20% within 5 times (100 msec). It will be.

  When the process proceeds to step S86, that is, when there are three or more cases exceeding 20% within a predetermined period, it can be said that a large change in channel quality has occurred frequently, To check the speed, change the estimated interval by half.

  Subsequently, the process proceeds to step S87, where it is determined whether or not the changed estimated interval is smaller than the shortest interval. If it is determined that the changed estimated interval is smaller than the shortest interval, the estimated interval is set to the shortest interval. Set (step S88), the process proceeds to step S85. Here, the shortest interval is the shortest interval time of CSI feedback defined by the LTE specification. For example, when the shortest period of CSI feedback is 1 subframe, the shortest estimated interval is 1 msec.

  On the other hand, when it is determined that the estimated interval after the change is equal to or longer than the shortest interval, the process proceeds to step S85 with the estimated interval after the change.

  If the process proceeds from step S82 to step S83, that is, if the number of cases exceeding 20% within the predetermined period is less than three, in step S83, the new estimated value and the previous estimated value are determined within the predetermined period. It is determined whether there are three or more cases where the difference is less than 5%. This is an operation for confirming that the channel quality has not changed much, not a large change in which the difference between the new estimated value and the previous estimated value exceeds 20%.

  The predetermined period here is the same as the predetermined period when it is determined whether or not it exceeds 20%. That is, both the case where the difference between the new estimated value and the previous estimated value is greater than 20% and less than 5% within the same predetermined period are determined.

  Then, if there are three or more cases within the predetermined period of time, the process proceeds to step S84, and if not, the process proceeds to step S85.

  When the process proceeds to step S84, that is, when there are three or more times within a predetermined period of time, it can be said that the channel quality does not change frequently, There is no need to check frequently, the estimated interval is changed to twice, and the process proceeds to step S85.

  In step S85, it is determined whether the currently ongoing communication session has ended. When the communication session is finished, the control of the dynamic adjustment of the channel estimation interval is also finished. On the other hand, if the communication session has not ended, the operations from step S82 are repeated.

  When the process proceeds from step S82 to step S83 and then from step S83 to step S85, that is, when the estimation interval is not changed within a predetermined period, the oldest recorded estimated value is discarded and the estimation interval is discarded. Accumulate new estimates obtained over time. Alternatively, all of the recorded estimated values, for example, all five times may be discarded, the recording may be reset, and recording may be performed again within a predetermined period.

  Note that the difference (20%, 5%) between the new estimated value and the previous estimated value is just an example, and it goes without saying that 20% may be 15%, and 5% may be 3%.

  In addition, the number of times (three times) that the difference between the new estimated value and the previous estimated value exceeds the predetermined value or falls below the predetermined value within a predetermined period is an example, and is set to 2 or 5 times. It goes without saying that it is also good.

  Note that the above-described method of dynamically adjusting the channel estimation interval can be applied to the case where channel estimation is performed simultaneously with the reception of CSI or the case where the channel estimation is performed independently of the reception of CSI.

  Note that the operation of dynamically adjusting the channel estimation interval described with reference to FIG. 14 is an operation performed by the control unit 242 of the processor 240 of the eNB 200.

  It should be noted that the present invention can be freely combined with each other within the scope of the invention, and each embodiment can be appropriately modified or omitted.

Claims (21)

A wireless communication device that communicates with a subordinate wireless communication device,
A controller that estimates a channel quality of a channel used for feedback of a signal from the subordinate radio communication apparatus, and performs scheduling for allocating radio resources to the subordinate radio communication apparatus in consideration of the estimated channel quality Prepared,
The controller is
Based on the estimated channel quality, it is determined whether or not the subordinate radio communication apparatus that has fed back the signal is a target of spatial multiplexing communication. A wireless communication apparatus that performs scheduling so that the subordinate wireless communication apparatus performs the spatial multiplexing communication. The controller is
Set a threshold value for determining the quality of the channel quality,
The radio communication apparatus according to claim 1, wherein when the estimated channel quality is equal to or higher than a threshold, the subordinate radio communication apparatus that has fed back the signal is targeted for the spatial multiplexing communication. The controller is
A first threshold value for determining whether the channel quality is good and a second threshold value higher than the first threshold value;
When the estimated channel quality is equal to or higher than the second threshold, the subordinate radio communication device that has fed back the signal is the target of the spatial multiplexing communication,
When the estimated channel quality is between the first threshold value and the second threshold value, it is conditionally subject to the spatial multiplexing communication,
The condition is
2. The wireless communication according to claim 1, wherein at least one of a degree of separation or orthogonality with a precoder corresponding to another subordinate wireless communication apparatus and a degree of necessity of the spatial multiplexing communication satisfy a specified value. apparatus. A wireless communication device that communicates with a subordinate wireless communication device,
A control unit that estimates channel quality of a channel used for feedback of a signal from the subordinate radio communication apparatus, and corrects a modulation / coding scheme for the subordinate radio communication apparatus in consideration of the estimated channel quality With
The controller is
When determining whether to correct the modulation / coding scheme for the subordinate radio communication apparatus that has fed back the signal based on the estimated channel quality, and correcting the modulation / coding scheme The modulation / coding scheme is selected so as to select a modulation / coding scheme having a transmission rate lower than the modulation / coding scheme determined based on the downlink channel quality status fed back from the subordinate radio communication apparatus. A wireless communication device to be corrected. The controller is
Set a threshold value for determining the quality of the channel quality,
The wireless communication apparatus according to claim 4, wherein when the estimated channel quality is equal to or higher than a threshold, the modulation / coding scheme for the subordinate wireless communication apparatus that has fed back the signal is not corrected. The controller is
A first threshold value for determining whether the channel quality is good and a second threshold value higher than the first threshold value;
When the estimated channel quality is equal to or higher than the second threshold, the modulation / coding scheme for the subordinate radio communication apparatus that has fed back the signal is not corrected,
When the estimated channel quality is between the first threshold value and the second threshold value, modulation / coding determined based on the downlink channel quality status fed back from the subordinate radio communication apparatus Select the first modulation / coding scheme that has a lower transmission rate than the scheme,
When the estimated channel quality is smaller than the first threshold value, the modulation / coding is performed so that the second modulation / coding scheme having a transmission rate lower than that of the first modulation / coding scheme is selected. The wireless communication apparatus according to claim 4, wherein the correction method is corrected. A wireless communication device that communicates with a subordinate wireless communication device,
A controller that estimates channel quality of a channel used for feedback of a signal from the subordinate radio communication apparatus, and corrects rank adaptation for the subordinate radio communication apparatus in consideration of the estimated channel quality;
The controller is
Based on the estimated channel quality, it is determined whether to correct the rank adaptation for the subordinate radio communication apparatus that has fed back the signal, and in the case of correcting the rank adaptation, the subordinate radio A wireless communication apparatus that corrects the rank adaptation so as to select a rank number smaller than the rank number corresponding to the channel information fed back from the communication apparatus. The controller is
Set a threshold value for determining the quality of the channel quality,
8. The wireless communication apparatus according to claim 7, wherein when the estimated channel quality is equal to or higher than a threshold, the rank adaptation for the subordinate wireless communication apparatus that has fed back the signal is not corrected. The controller is
A first threshold value for determining whether the channel quality is good and a second threshold value higher than the first threshold value;
When the estimated channel quality is equal to or higher than the second threshold, the rank adaptation for the subordinate radio communication device that has fed back the signal is not corrected,
When the estimated channel quality is between the first threshold value and the second threshold value, a first rank smaller than the rank number corresponding to the channel information fed back from the subordinate radio communication device Select the number,
8. The radio according to claim 7, wherein when the estimated channel quality is smaller than the first threshold, the rank adaptation is corrected so as to select a second rank number that is smaller than the first rank number. Communication device. A wireless communication device that communicates with a subordinate wireless communication device,
A controller that estimates a channel quality of a channel used for feedback of a signal from the subordinate radio communication device, and changes the transmission mode for the subordinate radio communication device in consideration of the estimated channel quality;
The controller is
Based on the estimated channel quality, it is determined whether to change the transmission mode for the subordinate radio communication apparatus that has fed back the signal, and when changing the transmission mode, a PMI (Precoding Matrix) Indicator) or a radio communication apparatus that selects a transmission mode that does not use a channel matrix and selects a transmission mode that uses the PMI or the channel matrix when the transmission mode is not changed. The controller is
Set a threshold value for determining the quality of the channel quality,
The wireless communication device according to claim 10, wherein when the estimated channel quality is equal to or higher than a threshold, the transmission mode for the subordinate wireless communication device that has fed back the signal is not changed. The controller is
A first threshold value for determining whether the channel quality is good and a second threshold value higher than the first threshold value;
When the estimated channel quality is equal to or higher than the second threshold, the transmission mode for the subordinate radio communication apparatus that has fed back the signal is not changed, and the transmission mode in closed-loop MIMO or MU-MIMO Select
When the estimated channel quality is between the first threshold value and the second threshold value, a transmission mode in open loop MIMO is selected for the subordinate radio communication device,
The radio communication device according to claim 10, wherein when the estimated channel quality is smaller than the first threshold value, a transmission mode in transmission diversity is selected for the subordinate radio communication device. A wireless communication device that communicates with a subordinate wireless communication device,
A controller that estimates a channel quality of a channel used for feedback of a signal from the subordinate radio communication apparatus, and performs scheduling for allocating radio resources to the subordinate radio communication apparatus in consideration of the estimated channel quality Prepared,
The controller is
Based on the estimated channel quality, it is determined whether or not to change the resource block allocation priority for the subordinate radio communication apparatus that has fed back the signal, and the resource block allocation priority is changed. If so, a wireless communication device that relatively changes an allocation priority of a resource block for the subordinate wireless communication device. The controller is
Set a threshold value for determining the quality of the channel quality,
The wireless communication device according to claim 13, wherein, based on the threshold value, it is determined whether to change a resource block allocation priority for the subordinate wireless communication device that has fed back the signal. The controller is
A first threshold value for determining whether the channel quality is good and a second threshold value higher than the first threshold value;
When the estimated channel quality is equal to or higher than the second threshold, the priority of the resource block allocation to the subordinate radio communication apparatus that has fed back the signal is not changed,
If the estimated channel quality is between the first threshold and the second threshold, the resource block allocation priority for the subordinate radio communication device is lowered to the first priority,
If the estimated channel quality is smaller than the first threshold, the resource block allocation priority for the subordinate radio communication device is lowered to a second priority lower than the first priority; The wireless communication apparatus according to claim 13. The controller is
The wireless communication apparatus according to claim 1, wherein the channel quality estimation interval is dynamically adjusted according to a change speed of the channel quality. A control method of signal processing in a wireless communication device that communicates with a subordinate wireless communication device,
(A) estimating a channel quality of a channel used for feedback of a signal from the subordinate radio communication device;
(B) performing scheduling for allocating radio resources to the subordinate radio communication apparatuses in consideration of the estimated channel quality,
The step (b)
Based on the estimated channel quality, it is determined whether or not the subordinate radio communication apparatus that has fed back the signal is a target of spatial multiplexing communication. A signal processing control method comprising a step of performing scheduling so as to perform the spatial multiplexing communication for a subordinate radio communication apparatus. A control method of signal processing in a wireless communication device that communicates with a subordinate wireless communication device,
(A) estimating a channel quality of a channel used for feedback of a signal from the subordinate radio communication device;
(B) taking into account the estimated channel quality, and correcting a modulation / coding scheme for the subordinate radio communication device; and
The step (b)
When determining whether to correct the modulation / coding scheme for the subordinate radio communication apparatus that has fed back the signal based on the estimated channel quality, and correcting the modulation / coding scheme Corrects the modulation / coding scheme to select a modulation / coding scheme having a transmission rate lower than the modulation / coding scheme determined based on the channel quality status fed back from the subordinate radio communication apparatus. A method for controlling signal processing, comprising the step of: A control method of signal processing in a wireless communication device that communicates with a subordinate wireless communication device,
(A) estimating a channel quality of a channel used for feedback of a signal from the subordinate radio communication device;
(B) taking into account the estimated channel quality, and correcting the rank adaptation for the subordinate radio communication device; and
The step (b)
Based on the estimated channel quality, it is determined whether to correct the rank adaptation for the subordinate radio communication apparatus that has fed back the signal, and in the case of correcting the rank adaptation, the subordinate radio A signal processing control method comprising the step of correcting the rank adaptation so as to select a rank number smaller than the rank number corresponding to the channel information fed back from the communication device. A control method of signal processing in a wireless communication device that communicates with a subordinate wireless communication device,
(A) estimating a channel quality of a channel used for feedback of a signal from the subordinate radio communication device;
(B) taking into account the estimated channel quality, and changing a transmission mode for the subordinate radio communication device; and
The step (b)
Based on the estimated channel quality, it is determined whether to change the transmission mode for the subordinate radio communication apparatus that has fed back the signal, and when changing the transmission mode, a PMI (Precoding Matrix) Indicator) or a signal processing control method including a step of selecting a transmission mode not using a channel matrix and selecting a transmission mode using a PMI or a channel matrix when the transmission mode is not changed. A control method of signal processing in a wireless communication device that communicates with a subordinate wireless communication device,
(A) estimating a channel quality of a channel used for feedback of a signal from the subordinate radio communication device;
(B) performing scheduling for allocating radio resources to the subordinate radio communication apparatuses in consideration of the estimated channel quality,
The step (b)
Based on the estimated channel quality, it is determined whether or not to change the resource block allocation priority for the subordinate radio communication apparatus that has fed back the signal, and the resource block allocation priority is changed. If so, a signal processing control method including a step of relatively changing a resource block allocation priority with respect to the subordinate radio communication apparatus.

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