JP4800438B2 - Base station apparatus and communication method - Google Patents

Description

  The present invention relates to a base station apparatus and a communication method in a mobile communication system of MIMO (Multi Input Multi Output) system.

  A multi-input multi-output (MIMO) communication method using a plurality of antennas between a base station and a user apparatus is known. In this method, it is possible to use a directional beam formed by multiplying a plurality of streams generated by duplicating a stream of a signal to be transmitted by a weighting factor corresponding to each of the streams. The transmission speed can be improved. The weighting coefficient used here is called a precoding vector or a precoding matrix.

3GPP, R1-074820, “Investigation on PMI Indication Schemes for Single-User MIMO Precoding in E-UTRA Downlink”

  In the above scheme, the user apparatus sets a precoding matrix based on the measurement of the common reference signal, generates precoding matrix indicator (PMI) information indicating the contents of the precoding matrix, and generates the precoding matrix indicator (PMI) information. PMI information is transmitted (feedback) to the base station. This feedback is performed periodically using an uplink physical control channel (Physical Uplink Control Channel: PUCCH), or using an uplink physical common channel (PUSCH) in response to a request from the base station. Done. The PMI information includes wideband PMI (common PMI) information representing the entire band allowed for the communication system, and PMI (frequency selective PMI) information for each subband in the band ( Non-patent document 1). The common channel may be referred to as a data channel.

  The base station processes a signal to be transmitted to the user apparatus using the PMI information received from the user apparatus, and transmits the signal using a directional beam suitable for the user apparatus. As described above, in the method using the PMI information, the PMI information needs to be shared by the base station and the user apparatus. When the PMI information is updated in accordance with a change in the radio propagation status, the updated PMI information is also updated. It must be shared between the two.

  However, depending on the radio propagation situation, the base station may erroneously receive the PMI information fed back from the user apparatus, and the PMI information may not be shared between the base station and the user apparatus. In this case, the base station uses PMI information different from the fed back PMI information, and the user apparatus receives a signal processed with PMI information different from the PMI information fed back by itself. The downlink shared channel cannot be processed appropriately.

  In order to solve such a problem, for example, if an error correction code such as a cyclic redundancy check (CRC) code is used, the base station can accurately detect the PMI information fed back from the user apparatus with a high probability. Can be received.

  However, as a result of the study by the inventors of the present invention, there is a case where the PMI information to be used does not match between the base station and the user apparatus even when the PMI information to be fed back is accurately received. It has been found. In some cases, more preferable PMI information should be shared between the base station and the user apparatus.

  The present invention provides a communication method capable of promoting effective use of PMI information in MIMO communication with feedback of PMI information, and a base station apparatus suitable for use of this communication method.

  According to the first aspect of the present invention, there is provided a base station apparatus in a multi-input multi-output (MIMO) mobile communication system using precoding. The base station apparatus is a precoding matrix indicator (PMI) indicating a precoding matrix generated in the user apparatus, and receives a PMI fed back from the user apparatus, and a signal to the user apparatus And a transmission unit for transmitting. The signal transmitted by the transmission unit includes information regarding whether or not the PMI information fed back by the user apparatus is followed after the lapse of a predetermined time from the timing when the PMI information is fed back by the user apparatus. .

  According to a second aspect of the present invention, there is provided the base station apparatus according to the first aspect, wherein the receiving unit receives a PUSCH including a PMI related to a subband.

  According to a third aspect of the present invention, there is provided the base station apparatus according to the first or second aspect, wherein the receiving unit receives a PUCCH including a broadband PMI.

  According to a fourth aspect of the present invention, there is provided a base station apparatus in a multi-input multi-output (MIMO) mobile communication system using precoding. The base station is a precoding matrix indicator (PMI) indicating a precoding matrix generated in the user equipment, and receives a PMI fed back from the user equipment, and a signal to the user equipment. A transmission unit for transmission. For the signal transmitted from the transmitter, in the user apparatus, channel estimation is performed using the PMI generated by the user apparatus and after a predetermined delay time has elapsed, and the transmission is performed. The signal transmitted by the unit includes information regarding whether or not the PMI information fed back by the user apparatus is being followed.

  According to a fifth aspect of the present invention, there is provided a base station according to the fourth aspect, wherein the transmitting unit provides the predetermined delay time through high layer signaling.

  According to the sixth aspect of the present invention, there is provided a communication method in a multi-input multi-output (MIMO) mobile communication system using precoding. This communication method is a precoding matrix indicator (PMI) indicating a precoding matrix generated in a user apparatus, and receiving a PMI fed back from the user apparatus, and transmitting a signal to the user apparatus And a step of performing. The signal transmitted in the transmitting step includes information on whether or not the PMI information fed back by the user apparatus is followed after a predetermined time has elapsed since the timing when the PMI information was fed back by the user apparatus. Yes.

  According to an embodiment of the present invention, a method for promoting effective use of PMI information in MIMO communication with feedback of PMI information, and a base station and user apparatus suitable for use of this method are provided. .

It is a schematic block diagram of the user apparatus by the 1st Embodiment of this invention. It is a time chart which shows typically communication between a user apparatus and a base station. It is a time chart which shows typically communication between the user apparatus of FIG. 1, and a base station. It is a schematic block diagram of the base station by the 2nd Embodiment of this invention. It is a time chart which shows typically communication between a base station and a user apparatus. It is a time chart which shows typically communication between the base station of FIG. 4, and a user apparatus. It is a schematic block diagram of the base station by the 3rd Embodiment of this invention. It is a schematic block diagram of the base station by the 4th Embodiment of this invention. It is a time chart which shows the communication method by the 4th Embodiment of this invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In all the drawings for explaining the embodiments, the same or corresponding reference numerals are used for those having the same or corresponding functions, and repeated description is omitted.

<First Embodiment>
First, a user apparatus according to a first embodiment of the present invention will be described with reference to FIG. As illustrated, the user apparatus 10 is configured as a two-reception antenna system having two antennas 101A and 102B.

  User apparatus 10 includes duplexers 102A and 102B, RF receiving circuits 104A and 104B, FFT units 106A and 106B, reception timing estimation unit 108, control channel decoding unit 110, PMI selection and CQI estimation unit 112, delay The circuit 114 includes a demodulation PMI accumulation unit 116, a demodulation PMI calculation unit 118, a channel estimation unit 120, a data channel signal detection unit 122, and a channel decoding unit 124.

  The RF receiving circuit 104A (104B) receives a signal from the base station via the receiving antenna 101A (101B) and the duplexer 102A (102B), and converts the received signal into a baseband digital signal. Signal processing. This signal processing may include, for example, power amplification, band limiting, and analog to digital conversion. Further, the RF reception circuit 104A (104B) outputs the signal-processed reception signal to the FFT unit 106A (106B) and the reception timing estimation unit 108.

  The reception timing estimation unit 108 estimates the reception timing of the signal-processed reception signal input from the RF reception circuits 104A and 104B. For this estimation, a cyclic prefix (CP) assigned by the base station may be used. The estimated reception timing is notified to the FFT units 106A and 106B.

  The FFT unit 106A (106B) performs Fourier transform on the reception signal input from the RF reception circuit 104A (104B) based on the reception timing notified from the reception timing estimation unit 108. Further, FFT section 106A (106B) outputs the received signal subjected to Fourier transform to control channel decoding section 110, PMI selection and CQI estimation section 112, channel estimation section 120, and data channel signal detection section 122.

  The control channel decoding unit 110 receives the Fourier-transformed received signal from the FFT unit 106A (106B), decodes the control channel included in the received signal, and data related to the PMI information used by the base station for signal transmission To extract. This data is necessary when demodulating the received signal. Specifically, this data indicates whether the PMI information used in the base station is PMI information fed back from the user apparatus or an explicit PMI number of the PMI information when other PMI information is used. Indicates which one. In the case of the explicit PMI number, the user apparatus 10 performs channel estimation of the received signal from the base station using the PMI information notified from the base station instead of the fed back PMI information. The explicit PMI number is notified when the base station has to use PMI information different from the PMI information fed back from the user apparatus 10 due to various causes. Except for such a rather irregular case, the fact that the fed back PMI information is followed is notified. Control channel decoding section 110 outputs the extracted PMI information to demodulation PMI calculation section 118.

  The PMI selection and CQI estimation unit 112 measures reception quality using a reference signal in the reception signal input from the FFT unit 106A (106B), generates channel quality information (Channel Quality Indicator: CQI), and generates PMI information. Set (select). As a result, a PMI suitable for the radio propagation status at that time is generated. Further, the PMI selection and CQI estimation unit 112 outputs the generated PMI information and the set CQI to the delay circuit 114.

  The delay circuit 114 receives the PMI information from the PMI selection and CQI estimation unit 112 and acquires a predetermined delay amount through, for example, high layer signaling from the base station. The delay circuit 114 delays the input PMI information by a predetermined delay amount and outputs the delayed PMI information to the demodulation PMI accumulation unit 116.

  The demodulation PMI storage unit 116 receives the PMI information from the delay circuit 114 and stores the input PMI information. Further, the demodulation PMI accumulation unit 116 can output the stored PMI information to the demodulation PMI calculation unit 118.

  The demodulation PMI calculation unit 118 receives the PMI information from the control channel decoding unit 110, and determines the PMI information used for demodulation based on the input PMI information. When the PMI information indicates that the PMI information fed back by the user apparatus in the base station is used, the demodulation PMI calculation unit 118 acquires the PMI information from the demodulation PMI storage unit 116. When the PMI information is an explicit PMI number, the demodulation PMI calculation unit 118 calculates PMI information to be used for demodulation based on the PMI number. Further, demodulation PMI calculation section 118 outputs the acquired or calculated PMI information to channel estimation section 120.

  The channel estimation unit 120 performs channel estimation on the received signal after the Fourier transform input from the FFT units 106A and 106B using the PMI information input from the demodulation PMI calculation unit, and the result is detected as a data channel signal. To the unit 122.

  The data channel signal detection unit 122 demodulates the signals input from the FFT units 106A and 106B using the channel estimation result input from the channel estimation unit 120. The demodulated signal is output from the data channel signal detection unit 122 and input to the channel decoding unit 124.

  The channel decoding unit 124 performs channel decoding on the demodulated signal input from the data channel signal detection unit 122, and reproduces the signal transmitted from the base station.

  Next, an example of communication performed between the user apparatus 10 and the base station according to the first embodiment of the present invention will be described. In order to explain the effect produced by the user apparatus 10, as a comparison, transmission / reception between a user apparatus that does not have the configuration of the user apparatus 10 and a base station in a precoding MIMO system will be described with reference to FIG. . In the following description, it is assumed that the PMI information notified from the base station to the user apparatus follows the PMI information fed back from the user apparatus.

  As shown in FIG. 2, first, PMI1 is fed back from the user apparatus (UE) to the base station (NodeB) at time t1. Prior to feedback, the PMI1 is generated by the user apparatus as a precoding matrix indicator indicating a precoding matrix suitable for the downlink based on the reception quality of the reference signal in the received signal received from the base station. Has been. In addition, the user apparatus transmits PMI1 and simultaneously stores PMI1 in the demodulation PMI accumulation unit in the user apparatus. The PMI 1 stored in the PMI accumulation unit is then referred to when the user apparatus receives data from the base station, and is used for processing such as data decoding.

  When the base station receives PMI1 at time t2 when a predetermined delay Δ has elapsed from time t1, the base station decodes the received PMI1 to obtain a precoding matrix. This precoding matrix is assigned an index of PMI1 and is stored in the PMI accumulation unit in the base station. Here, since various processes such as decoding of PMI1 are performed, time T necessary for the various processes elapses from reception of PMI1 to storage of PMI1.

  Next, the base station transmits a signal to the user apparatus that has fed back PMI1 at time t3. At this time, the base station refers to the PMI accumulation unit, acquires PMI1 to be used for transmission to this user apparatus, and weights each stream of the signal to be transmitted using a precoding matrix corresponding to PMI1. . After that, the base station performs predetermined signal processing such as signal multiplexing and transmits the signal to the user apparatus.

  Next, at time t4 when a predetermined delay Δ has elapsed since the time when the base station transmitted the signal (time t3), the user apparatus receives the signal. The user apparatus decodes the signal using PMI1 stored in its own PMI accumulation unit. In this case, since the PMI information used in the base station is PMI1, and the PMI information used in the user apparatus is also PMI1, normal reception is performed.

  At time t5, when the base station transmits a signal to the same user apparatus, PMI1 is stored in the PMI accumulating unit of the base station (as PMI information for the user apparatus). After being weighted, a signal is transmitted to the user equipment. Similarly to the above, since the user apparatus knows that the PMI information to be used is PMI1, normal reception is performed.

  Subsequently, at time t7, the user apparatus feeds back PMI2 different from PMI1. The change (update) from PMI1 to PMI2 is necessary due to a change in the radio propagation status or the like, and PMI2 is PMI information that the user apparatus determines to be optimal at that time. Further, the user apparatus stores the PMI2 in its own PMI accumulation unit almost simultaneously with the transmission of the PMI2. Note that the feedback of the PMI information may be periodically performed using the PUCCH, or may be performed using the PUSCH in response to a request from the base station.

  At time t8 when a predetermined delay Δ has elapsed from time t7, the fed back PMI2 is received by the base station. Thereafter, the PMI2 is decoded and the like, and after the time T has elapsed since the reception of the PMI2, the PMI2 is stored in the PMI accumulation unit of the base station.

  After the PMI information in the PMI storage unit of the base station is updated to PMI2, PMI2 is used for weighting and transmission from the base station to the user apparatus is performed. For example, when transmitted from the base station at time t11 and received by the user apparatus at time t12, PMI2 is used in the base station, and PMI2 is also used in the user apparatus. Therefore, the user device is successfully received.

  However, when the base station transmits a signal to the user apparatus before the time T has elapsed after receiving the PMI2, the PMI1 is still stored in the PMI accumulation unit of the base station. PMI1 is used. On the other hand, the user apparatus that receives the signal stores PMI2 in its own PMI accumulation unit, and thus demodulates the received signal using PMI2. As described above, since the PMI information used in the base station is different from the PMI information used in the user apparatus, the user apparatus cannot appropriately process the signal. That is, when the base station transmits before the update of the PMI information is completed, there is a problem in that the PMI information does not match between the base station and the user apparatus.

  Next, how this problem is solved by the user device 10 according to the first embodiment of the present invention will be described with reference to FIGS.

  In the user apparatus 10, the PMI information selected by the PMI selection and CQI selection unit 112 (FIG. 1) is input to the demodulation PMI accumulation unit 116 with a delay of a predetermined delay amount (T + 2Δ) by the delay circuit 114. The That is, in FIG. 2, PMI1 is stored in the PMI accumulator at the time point (T1) when PMI1 is fed back from the user apparatus, whereas as shown in FIG. 3, the user apparatus 10 according to the present embodiment of the present invention is used. Then, the PMI 1 is stored in the demodulation PMI accumulating unit 116 after a predetermined delay amount (T + 2Δ) from the time t 1. Further, the PMI selection and CQI estimation unit 112 of the user apparatus 10 detects that the PMI information should be changed from PMI1 to PMI2, and also when the PMI2 is fed back to the base station, it is similarly delayed by a predetermined delay amount ( The PMI information in the demodulation PMI storage unit 116 is updated to PMI2 after a delay of T + 2Δ from t7.

  Referring to FIG. 2 and FIG. 3, when the base station transmits a signal to the user apparatus 10 at time t9, the update to PMI2 is not finished at time t9, so PMI1 is used and the signal to the user apparatus 10 is transmitted. Is sent. Referring to FIG. 3, at time t10 when the user apparatus receives the signal, demodulation PMI accumulating unit 116 of user apparatus 10 stores PMI1. This is because the delay circuit 114 does not immediately update to PMI2 at time t7 when the user apparatus 10 feeds back PMI2, but causes a delay of T + 2Δ. Therefore, the PMI1 used by the base station matches the PMI1 stored in the demodulation PMI accumulation unit 116 of the user apparatus 10, and the user apparatus 10 can receive appropriately. Thus, according to the user apparatus 10 of the present embodiment, the base station that has received the update of the PMI information transmits using the PMI information before the update before completing the process for the update. Even in this case, the PMI information can be matched between the base station and the user apparatus, and thus communication failure due to the PMI information mismatch can be prevented.

  Note that the time T required for decoding the PMI information or the like may be determined in advance between the base station and the user apparatus as a constant value, and may vary depending on the amount of signal processing in the base station. For example, the notification may be made by high layer signaling. The signal propagation delay Δ may be calculated based on the subband frame number used for feedback of the PMI information. 2 and 3, for the sake of convenience, the propagation delay Δ is the same for both upstream transmission and downstream transmission, but it may be different.

<Second Embodiment>
Next, a base station according to the second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a schematic diagram illustrating a configuration of a base station according to the second embodiment of the present invention. As illustrated, the base station 40 is configured as an eight antenna system having eight antennas 402A to 402H. The base station 40 includes N buffers 414 _{1 to} 412 _N , N PMI information multiplexers 414 _{1 to} 414 _N , a scheduler 416, a channel encoder 418, a data modulator 420, and precoding Matrix (PM) multiplication unit 422, common reference signal multiplexing units 424A to 424H, fast inverse Fourier transform (IFFT) units 426A to 426H, CP applying units 428A to 428H, RF transmission circuits 430A to 430H, duplexers 404A to 404H, antenna combining section 406, demodulation / decoding section 408, control channel feedback PMI / frame number storage section 432, data channel feedback PMI / frame number storage section 434, PMI / CQI selection section 436, including.

The buffers 412 _{1 to} 412 _N store transmission data to be transmitted to each of N user apparatuses (not shown) existing in the cell of the base station 40.

PMI information multiplexing unit ₄₁₄ 1 _{~414 N} is respectively corresponding N buffers ₄₁₁ 1 _{~412 N} connections, enter the corresponding transmission data. Also, the PMI information multiplexing units 414 _{1 to} 414 _N receive PMI information from a PMI / CQI selection unit 436 (to be described later), and multiplex them into shared data channels of transmission data respectively input from the buffers 411 _{1 to} 412 _N. Thus, a transmission signal corresponding to each user apparatus is generated.

  Modulation scheme / coding rate selection section 410 receives CQI from PMI / CQI selection section 436 (described later), and based on the CQI, modulation scheme and coding rate optimum for transmission from base station 40 to the user apparatus. Select. Based on the selection result, modulation scheme / coding rate selection section 410 generates modulation method information indicating the selected modulation method, and outputs the modulation method information to data modulation section 420. Furthermore, based on the selection result, modulation scheme / coding rate selection section 410 generates scheme information indicating the selected channel coding scheme, and outputs the scheme information to channel coding section 418.

The scheduler 416 receives transmission signals transmitted from the PMI information multiplexing units 414 _{1 to} 414 _N to N user apparatuses, and allocates each transmission signal to a radio resource.

  The channel coding unit 418 receives the transmission signal from the scheduler 416 and receives the system information indicating the channel coding system from the modulation system / coding rate selection unit 410. Further, the channel coding unit 418 performs channel coding on the transmission signal by a method indicated by the method information. Further, channel coding section 418 outputs the channel-coded transmission signal to data modulation section 420.

  Data modulation section 420 receives a channel-coded transmission signal from channel coding section 418 and receives modulation method information indicating a modulation method from modulation scheme / coding rate selection section 410. Data modulation section 420 modulates the input transmission signal by the modulation method indicated by the modulation method information. Further, the data modulation unit 420 outputs the modulated transmission signal to the PM multiplication unit 422.

  The PM multiplier 422 receives the modulated signal from the data modulator 420, duplicates the input signal, and generates eight transmission signals equal to the number of antennas. That is, eight transmission signals transmitted from each of the eight antennas 402A to 402H are generated. In other words, the PM multiplication unit 422 has a function as a distributor. PM multiplier 422 receives PMI information from PMI / CQI selector 436 and multiplies the generated transmission signal by a precoding matrix. As a result, the shared data channel is transmitted from the eight antennas 402A to 402H by a directional beam having strong directivity in the direction in which the user apparatus that is the transmission destination is located.

  Each of the eight transmission signals multiplied by the precoding matrix generated in PM multiplication section 422 is then output to common reference signal multiplexing sections 424A to 424H. Each of the common reference signal multiplexing units 424A to 424H multiplexes the common reference signal to the transmission signal input from the PM multiplication unit 422, and outputs the transmission signal obtained by multiplexing to the corresponding IFFT units 426A to 426H.

  IFFT sections 426A to 426H perform fast inverse Fourier transform on the transmission signals input from common reference signal multiplexing sections 424A to 424H, and output the converted transmission signals to CP assignment sections 428A to 428H, respectively. CP assigning sections 428A to 428H add a cyclic prefix (CP) to the input signal, and output the transmission signals to which the CP is added to RF transmitting circuits 430A to 430H, respectively. The RF transmission circuits 430A to 430H perform processing (digital / analog conversion, band limitation, power amplification, etc.) for transmitting the input signal. The processed signals are transmitted from antennas 402A to 402H via duplexers 404A to 404H.

The output unit of the base station 40 is configured by the elements from the buffers 412 _{1 to} 412 _N described above to the RF transmission circuits 430A to 430H. Next, elements constituting the receiving unit will be described. In the following description, the case of transmission to one user apparatus is illustrated.

  The antenna combining unit 406 inputs signals transmitted from the user apparatus (received signals for the base station 40) from the antennas 402A to 402H via the duplexers 404A to 404H. Further, antenna combining section 406 combines these signals and outputs the combined signal to demodulation / decoding section 408.

  The demodulation / decoding unit 408 demodulates / decodes the combined signal input from the antenna combining unit 406 by a predetermined demodulation / decoding method. Also, the demodulation / decoding unit 408 uses PMI information fed back using an uplink physical control channel (PUCCH), CQI corresponding to the PMI information, and feedback thereof from the demodulated / decoded signals. The frame number of the frame (that is, the time of feedback), the PMI information fed back using the uplink data channel (PUSCH), the CQI corresponding to this PMI information, and the frame number of the frame used for the feedback Extract. Further, demodulation / decoding section 408 outputs PMI information, CQI and frame number of PUCCH to control channel feedback PMI / CQI / frame number storage section 432 (hereinafter referred to as storage section 432), and PSCH PMI information, CQI. , And the frame number are output to the data channel feedback PMI / CQI / frame number accumulating unit 434 (hereinafter referred to as accumulating unit 434).

  The accumulation unit 432 receives the PMI information, CQI, and frame number of the control channel (PUCCH) from the demodulation / decoding unit 408 and stores them. Further, the accumulation unit 432 can output the stored PMI information, CQI, and frame number of the PUCCH to the PMI / CQI selection unit 436.

  The accumulation unit 434 receives the PMI information, CQI, and frame number of the data channel (PUSCH) from the demodulation / decoding unit 408 and stores them. Further, the accumulation unit 434 can output the stored PSCH PMI information, CQI, and frame number to the PMI / CQI selection unit 436.

  The PMI / CQI selection unit 436 receives the PMI information, CQI, and frame number of the control channel (PUCCH) from the storage unit 432. Also, the PMI / CQI selection unit 436 receives the PMI information, CQI, and frame number of the data channel (PUSCH) from the storage unit 434. Furthermore, the PMI / CQI selection unit 436 can select which PMI information should be used based on the input PMI information and the frame number. This selection will be described later.

Also, the PMI / CQI selection unit 436 outputs the selected PMI information to the PMI multiplexing units 414 _{1 to} 414 _N and the PM multiplication unit 422, and selects the CQI corresponding to the selected PMI information as a modulation scheme / coding rate selection. Output to the unit 410.

  Next, an example of communication performed between the base station 40 and the user apparatus will be described according to the second embodiment of the present invention. However, for comparison, first, transmission / reception in a MIMO system of a precoding scheme between a user apparatus that does not have the configuration of the user apparatus 10 and a base station will be described with reference to FIG. In FIG. 5 and FIG. 6 referred to in the following description, the signal propagation delay Δ is ignored. Further, the base station (base station 40) is assumed to follow the PMI information fed back from the user apparatus. Furthermore, the user apparatus which communicates with a base station (base station 40) may be the user apparatus 10 according to the first embodiment.

  Referring to FIG. 5, the user apparatus (UE) performs feedback of non-periodic frequency selective PMI1 using PUSCH at time t1. That is, there is a request from the base station to feed back PMI information including PMI information related to a predetermined subband, and in response to the request, feedback of PMI information is performed at time t1.

  Further, at time t2 immediately after time t1, the user apparatus feeds back wideband (common to all bands) PMI2 as feedback of periodic PMI information using PUCCH. That is, in the illustrated example, it is agreed between the user apparatus and the base station that wideband PMI information should be fed back at a constant cycle using PUCCH, and feedback according to this agreement is performed at time t2. It is done in When receiving the PMI2, the base station performs a predetermined process to acquire the PMI2, and updates the PMI information in the PMI accumulation unit to the PMI2.

  Thereafter, when the base station transmits a signal to the user apparatus at time t3, the base station uses the updated PMI information. That is, as a rule, the latest PMI information is used. In the illustrated example, PMI2 is used, and the frequency selective PMI information using the PUSCH requested by the base station is not used. Therefore, the base station cannot use the frequency-selective PMI information even though it has requested it. Therefore, there arises an inconvenience that more optimal weighting cannot be performed.

  According to the base station 40 according to the second embodiment of the present invention, such inconvenience is solved as follows. Referring to FIG. 6, since PMI1 fed back at time t1 is fed back using PUSCH, it is stored as PMI-A in accumulating unit 434 (FIG. 4). At this time, the frame number of the frame used for feedback of PMI 1 is also stored in the storage unit 434.

  Thereafter, PMI2 fed back using PUCCH at time t2 is stored as PMI-B in accumulation unit 432 (FIG. 4). The frame number of the frame used for PMI2 feedback is also stored in the storage unit 432.

Next, when the base station 40 transmits a signal to the user apparatus at time t3, the PMI information selected by the PMI / CQI selection unit 436 is used. This selection is performed as follows, for example. First, in the PMI / CQI selection unit 436, the elapsed time from the time when PMI1 is fed back to the time of data transmission (downlink transmission) is T1, and the elapsed time from the time when PMI2 is fed back to the time of data transmission is T2. Is calculated. These calculations may be performed based on the frame numbers input from the storage units 432 and 434. next,
L = a ^T1 -b ^T2 (0 <a <1, 0 <b <1) Formula (1)
The L value represented by is calculated. Next, it is determined whether or not the L value is 0 or more. If it is 0 or more, PMI-A is selected, and if it is less than 0, PMI-B is selected. Here, a and b are forgetting factors, and may be appropriately determined according to, for example, a radio propagation situation. According to such a selection, the feedback of PMI1 through PUSCH can be preferentially used even when the feedback of PMI2 through PUCCH precedes. When using the PUSCH, the user equipment can feed back frequency selective PMI (PMI for each subband) information as PMI-A, and the base station 40 can use these to more appropriately Scheduling can be performed.

  As described above, in the base station 40 according to the present embodiment, even when feedback of frequency selective PMI information using PUSCH precedes feedback of PMI information common to all bands using PUCCH, When it is assumed that the time difference is small and the radio propagation situation does not change greatly, it is possible to preferentially use the PMI information fed back through the PUSCH over the latest PMI information fed back through the PUCCH. Also, the latest PMI information can be used when it is assumed that the time difference is large and the radio propagation situation has changed significantly. Therefore, according to the base station 40 according to the present embodiment, an effect of enabling more preferable scheduling is exhibited.

  Note that the PMI information to be used may be selected based on the difference between T1 and T2. For example, when T1> T2 and T2-T1 is equal to or shorter than a predetermined time, PMI-A may be used instead of PMI-B. That is, when PMI-B is received immediately after receiving PMI-A and the time difference between the two is short, it is assumed that the propagation environment between the base station and the user apparatus has not changed so much. Therefore, it is beneficial to use PMI-A fed back through PUSCH (eg, frequency selective) rather than PMI-B fed back through PUCCH (eg, broadband).

  Further, although the elapsed times T1 and T2 are calculated from the frame number of the frame used for feedback of the PMI information, the present invention is not limited to this, and the time when the base station grasps the reception of the PMI information may be used as the starting time. That is, any method may be used as long as it is possible to quantitatively determine which of PMI information feedback using PUCCH and PMI information feedback using PUSCH is first.

  Furthermore, although an example in which PMI information fed back using PUSCH is prioritized has been described, the present invention is not limited to this, and feedback is performed through PUCCH when feedback using PUSCH is performed after feedback using PUCCH. PMI information may be prioritized. This is because the base station 40 according to the second embodiment has a control channel feedback PMI / CQI / frame number accumulation unit 432 and a data channel feedback PMI / CQI / frame number accumulation unit 434, and Since PMI information is stored, this can be realized. Also from this, the advantage of the mobile station 40 of this embodiment is understood.

  Note that the PMI information selected by the base station 40 may be explicitly notified to the user apparatus.

<Third Embodiment>
Next, a base station according to the third embodiment of the present invention will be described with reference to FIG. FIG. 7 is a schematic diagram illustrating a configuration of a base station according to the third embodiment of the present invention. As is apparent from a comparison of FIG. 7 with FIG. 4, the base station 70 according to the third embodiment includes the control channel feedback PMI / CQI / frame number accumulation unit 432 and the data channel feedback of the base station 40 according to the second embodiment. It is mainly different from the base station 40 according to the second embodiment in that instead of the PMI / frame number accumulation unit 434, an all-band common PMI / CQI accumulation unit 732 and a frequency selective PMI / CQI accumulation unit 734 are provided. . Hereinafter, the difference will be mainly described.

  The demodulation / decoding unit 708 of the base station 70 demodulates / decodes the combined signal input from the antenna combining unit 706 by a predetermined demodulation / decoding method. The demodulating / decoding unit 708 also uses PMI information (wideband PMI information) common to all bands representing the channel quality of the entire system band, and the channel used for feedback of the PMI information, among the demodulated / decoded signals. Average channel quality information (CQI). Further, demodulation / decoding section 708 extracts frequency selective PMI information (PMI information for each subband) and an average CQI of the channel used for feedback of this PMI information.

  Further, the demodulation / decoding unit 708 outputs the PMI information common to all bands and the average CQI related thereto to the all-band common PMI / CQI accumulating unit 732, and the frequency selective PMI information and the average CQI related thereto. Is output to the frequency selective PMI / CQI accumulating unit 734.

  The all-band common PMI / CQI accumulating unit 732 receives the PMI information common to all the bands and the average CQI related thereto from the demodulation / decoding unit 708 and stores them. Further, the all-band common PMI / CQI accumulating unit 732 can output the stored all-band common PMI information and the average CQI related thereto to the PMI / CQI selecting unit 736.

  The frequency selective PMI / CQI accumulating unit 734 receives the frequency selective PMI information and the average CQI related thereto from the demodulation / decoding unit 708 and stores them. Further, the frequency selective PMI / CQI accumulating unit 734 can output the stored frequency selective PMI information and the average CQI related thereto to the PMI / CQI selecting unit 736.

  The PMI / CQI selection unit 736 inputs the PMI information common to all bands and the average CQI related thereto from the all-band common PMI / CQI storage unit 732. Also, the PMI / CQI selection unit 736 receives the frequency selective PMI information and the average CQI related thereto from the frequency selective PMI / CQI storage unit 734. Further, the PMI / CQI selection unit 736 can select which of PMI information common to all bands and frequency selective PMI information should be used based on the two average CQIs input.

For example, the PMI / CQI selection unit 736 has a difference between the average CQI1 of the channel used for feedback of PMI information common to all bands and the average CQI2 of the channel used for feedback of frequency selective PMI information:
D = CQI1-CQI2 Formula (2)
Is equal to or greater than a predetermined value X, PMI information common to all bands is selected, and if it is less than the predetermined value X, frequency selective PMI information is selected. The X value may be 0 dB, for example.

Also, the PMI / CQI selection unit 736 outputs the selected PMI information to the PMI information multiplexing units 714 _{1 to} 714 _N and the PM multiplication unit 722, and selects a CQI corresponding to the selected PMI information as a modulation scheme / coding rate selection. Output to the unit 710.

  In the base station 70 according to the present embodiment configured as described above, the PMI / CQI selection unit 736 compares two average CQIs and selects PMI information based on the comparison result. Therefore, transmission from the base station 70 to the user apparatus is not limited to the latest PMI information, but PMI information fed back through a channel with good radio propagation conditions is used. As a result, the frequency with which the user apparatus erroneously receives the PMI information used in the base station 70 is reduced, and the mismatch of PMI information between the base station 70 and the user apparatus is reduced.

  Note that the PMI information selected by the base station 70 may be explicitly notified to the user apparatus.

<Fourth Embodiment>
Next, a base station according to the fourth embodiment of the present invention is described. The base station according to the fourth embodiment is different from the second embodiment in that the request timing of feedback of aperiodic PMI (preferably frequency selective PMI) information performed from the base station to the user apparatus is adjusted. It is mainly different from the base station 40 according to the form. Hereinafter, the difference will be mainly described.

  When the base station 40 requests the user apparatus to perform aperiodic PMI information feedback, the scheduler 416 of the base station 40 determines that the feedback from the user apparatus in response to the request is a periodic feedback. The timing for transmitting the request is adjusted so that the request is performed within a predetermined time range including the time point.

  Specifically, as illustrated in FIG. 8, the base station 40 according to the present embodiment includes a control channel feedback time / period accumulation unit 438 for the user with the user number N and an aperiodic PMI feedback request determination unit for the same user. 440 and a downlink control channel generation unit 442 are further included.

  The control channel feedback time / cycle storage unit 438 stores feedback time (cycle) for each user. This feedback time is determined when communication is started between the base station 40 and the user apparatus. Based on the success or failure of receiving the PMI information from the user apparatus and the CQI included in the received signal, the feedback request determination unit 440, for example, for the user apparatus, aperiodic frequency selectivity using PUSCH It is determined whether feedback of PMI information should be requested. When the downlink control channel generation unit 442 determines that the feedback request determination unit 440 should request, the downlink control channel generation unit 442 requests feedback from the user apparatus using the UL grant. Therefore, when a control channel is generated for a certain user in the base station 40, it is determined by the feedback request determination unit 440 whether or not a non-periodic feedback of PMI should be requested. The feedback request stored in the control channel feedback time / period storage unit 438 corresponding to the user is referred to, and a feedback request is made at an appropriate timing.

  Here, the predetermined time range may include, for example, zero. That is, as shown in FIG. 9, periodic feedback and feedback in response to a request may be performed at the same time. Further, the predetermined time range may be a range in which the L value is 0 or more in the determination based on Expression (1) using time lapses T1 and T2 (FIG. 6). According to this, even when the base station requests the aperiodic PMI information feedback and the subsequent periodic PMI information feedback is performed, the PMI by the aperiodic feedback is used. Information will be used. In aperiodic feedback, since frequency selective PMI information using PUSCH is usually fed back, this is prioritized and more suitable scheduling is possible.

  Also, for example, when feedback of aperiodic PMI information is performed within a predetermined time range from the time when feedback of periodic PMI information is performed, priority is given to PMI information based on aperiodic feedback. You may negotiate beforehand between the base station 40 and a user apparatus.

  For convenience of explanation, the present invention is described in several embodiments, but the division of each embodiment is not essential to the present invention, and two or more embodiments may be used as necessary.

  DESCRIPTION OF SYMBOLS 10 ... User apparatus, 40, 70 ... Base station, 112 ... PMI selection part and CQI estimation part, 114 ... Delay circuit, 116 ... Demodulation PMI storage part, 118 ... Demodulation PMI calculation unit, 120 ... channel estimation unit, 408 ... demodulation / decoding unit, 410 ... modulation scheme / coding rate selection unit, 422 ... PM multiplication unit, 432 ... control channel feedback PMI / CQI / frame number accumulation unit, 434... Data channel feedback PMI / CQI / frame number accumulation unit, 436... PMI / CQI selection unit, 708... Demodulation / decoding unit, 710. Code rate selection unit, 732... All-band common PMI / CQI accumulation unit, 734... Frequency selective PMI / CQI accumulation unit, 736... PMI / CQI selection unit.

Claims (6)

A base station apparatus in a mobile communication system of a multi-input multi-output (MIMO) system using precoding,
A precoding matrix indicator (PMI) indicating a precoding matrix generated in the user apparatus, and a receiver that receives the PMI fed back from the user apparatus;
A transmission unit for transmitting a signal to the user device,
The signal transmitted by the transmission unit includes information regarding whether or not the PMI information fed back by the user apparatus is followed after the lapse of a predetermined time from the timing when the PMI information is fed back by the user apparatus. A base station apparatus.   The base station apparatus according to claim 1, wherein the receiving unit receives a PUSCH including a PMI related to a subband.   The base station apparatus according to claim 1, wherein the reception unit receives a PUCCH including a broadband PMI. A base station apparatus in a mobile communication system of a multi-input multi-output (MIMO) system using precoding,
A precoding matrix indicator (PMI) indicating a precoding matrix generated in the user apparatus, and a receiver that receives the PMI fed back from the user apparatus;
A transmission unit for transmitting a signal to the user device,
For the signal transmitted from the transmission unit, in the user apparatus, the PMI generated by the user apparatus and using a PMI that has been passed after a predetermined delay time is used to perform channel estimation,
The base station apparatus characterized in that the signal transmitted by the transmission unit includes information regarding whether or not the PMI information fed back by the user apparatus is followed.   The base station apparatus according to claim 4, wherein the transmission unit provides the predetermined delay time through high layer signaling. A multi-input multi-output (MIMO) type mobile communication system using precoding,
Receiving a PMI that is a precoding matrix indicator (PMI) indicating a precoding matrix generated in the user equipment and fed back from the user equipment;
Transmitting a signal to the user equipment,
The signal transmitted in the transmitting step includes information on whether or not the PMI information fed back by the user apparatus is followed after a predetermined time has elapsed since the timing when the PMI information was fed back by the user apparatus. A communication method characterized by comprising:

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